I’m going to attempt to answer your question for real. I have never had to cremate a person, but I have cremated pets before. One time I think I may have gotten a symbolic collection of ashes, and the other time I was pretty sure I got my exact cat. The difference was visible in their system.

The first time I did not ask many questions, and I ended up with a bag of ashes that had a sticky note with my name on it. It would have been very easy for the wrong bag to be placed with my name, or for the notes to fall off and get mixed up. It was clear that accuracy was secondary to creating a chance for closure. They were very nice and professional, it was just clear that they had not felt it necessary to have an iron clad ash delivery system.

The second time I needed to cremate a pet, I asked a lot more questions, and all were answered without any surprise. Considering the type of business it is, it is always ok to ask a lot of questions about the process.

They put a tracking barcode on my deceased kitty as well as on the body bag he was placed in. When I picked up the ashes days later, the same barcodes were on the tightly sealed bag as well as on the carrying bag, plus they had his collar and a pawprint memorial in the bag too. They could have given me random ashes still, but the care that they clearly put into their system gave me a strong feeling that they had held up their end of the bargain.

The sad truth is that there is probably no way to be 100% sure, and it is likely normal for some ashes to get left behind while others may be unintentionally scooped in. The best you can do is make sure that you ask all the questions you need to (don’t let anxiety shut you up), and try to pick a place that will treat your loved one with dignity.

I was a funeral director in Ontario, Canada. The law here is that the contract you sign with the crematorium will have a cremation number which will be stamped into a metal disk and that disk will be placed with the remains. After cremation, the disk will be in the cremated remains. People who receive the cremated remains can check that the number on the disk matches the number on the contract they signed.

This system stops honest mistakes but nothing stops people from intentionally swapping disks. Say a funeral home worker is filling urns with a batch of cremated remains they recieved from the crematorium. They accidentally put remains A into the urn for family B and remains B into the urn for family A. The worker should swap the remains...but swaping the disks is easier. Most people I've worked with would do the right thing but the system still relies on people being honest.

I think it depends entirely on the integrity of the cremator. I have a good friend who does pet cremations. He cremated one of my pets and told me that he had a hell of a hard time getting the bag of ashes into the box I gave him. I laughed and asked him why he didn't just pour some out so the bag would fit more easily. Who would know? Who would care if there were a few grams missing? Especially if the reason was that the client-provided box was too small. But he was genuinely shocked and said he would never do that.

Cremation doesn't burn everything to ash. Pieces of bone are left intact and must be mechanically pulverized to make the remains a powder.

When my dad's dog was cremated many years ago, the remains they gave us were partially ash, but the larger pieces hadn't been pulverized. It still had many intact pieces of bone. We could see evidence of some injuries and degenerative disease the dog had experienced in his hip and spine.

I'm not sure how many people would be down for rooting through their pet's remains for proof that it is the right animal.

You have to cremate them yourself. Sorry.

You get a stone with a number carved in it beforehand. You put the stone with the deceased body. Afterwards that stone is in the urn.

Edit: bonus fact, if the person was heavy, their ashes will be too.

Taste test

You can tell by the taste

Well, you likely can't, since that would require witnessing the entire process. You aren't likely going to be allowed to do that. Afaik, no state in the US allows anyone other than the people running the crematorium to be present, and that have to have various certifications to do the job.

Which is where you can reach as close to certainty as it can get.

You look at the laws and regulations for the state you're in. The states that have stricter requirements are going be essentially certain as long as they've been inspected regularly. Most places just aren't going to risk being shut down or fined just to move a little faster.

The process for certification in some states even specifies, or requires the crematorium to detail, the exact process used to insure the right remains go in the fire, and that all reasonable steps are taken to remove all of the remains before further processing.

The stricter the state, the more certain you can be. Iirc NY is one of the tightest ones, and there's something about the tools used to remove remains having to do the job, and how much is acceptable to be left behind. And, iirc, even the remains that can't be sent out after that have to be cleaned up in a way so as to avoid mixing remains with the next. Maybe it's California that goes that strict? Can't remember exactly, but the process is pretty rigorous.

Other states just specify "all reasonable effort" be used, and don't require the plan for more to ensure no mixing happens.

There's a mortician that does a YouTube channel about funerary issues, Caitlyn Doughty. She's pretty good about explaining things in an accessible but detailed manner. That link is to her video on cremation, but her other stuff is fascinating too.

Fwiw, I looked into all this stuff over a decade ago as research for a book series I was planning. Talked to medical examiners, morticians, and other death related jobs and the people that do them. There are places that cut corners, but even those tend to be reliable enough that what you get is almost entirely your loved one. They just skip some of the cleaning steps, so there's "leftovers" in the crematorium or other workspaces. But it's fairly rare. Most of the people doing the work are aware of not only how important it is to the bereaved, but how much it would cost for them to fuck up. So even the big chains don't cut too many corners.

It was kinda reassuring talking to those folks. They're talking to me off the record, no recordings, no written notes, no names. So they were all pretty open about mistakes happening, and the industry problems. They weren't afraid to tell stories about them fucking up, and that fuck ups weren't as bad as you'd think. We're talking more about some of the remains being unrecoverable, but not all. Stuff like cleaning agents spilling, unexpected problems during the process. But none of it would result in someone getting the wrong remains entirely.

For that to happen, you'd have to have someone intentionally ignoring procedure, ignoring all the verification, and just dumping a body in essentially at random. It's not that it couldn't happen, it's more that it would take more work to cause it than it would to do it right.

I wanna say there was a case of it in Virginia? Might have been North Carolina. But it was small crematory, and they got a lot of bodies in at once, and paperwork got fucked up enough that the guy telling the story wasn't ever able to sort things out and be certain everyone got the right remains. He was relatively confident it got sorted out, but not 100%.

And rumors do get told about things going wrong after big disasters just because workers are overwhelmed. But they're rumors, and it was always "I heard from this guy I met at a conference" kind of stories.

I intend to be cremated. I consider the risk of errors to be so marginal as to be irrelevant. Mind you, I don't care for my own sake at all. Idgaf what happens to my corpse. Feed it to the birds, stuff it and mount out, whatever. But cremation is cheaper than other options, and I'm not willing to jump through the hoops to donate my body to anything.

Give your loved one a lick before and after cremation. Fool proof method.

Basically, you can't be sure. More of a problem with pets. When I had a pet cremated, they sent a video of the entire process up to and including them putting the ashes into the container. I was kind of like wtf? And they said I didn't have to watch it, and they were happy to not give me the video, but that people were often concerned about just getting random ashes and that it was apparently common for some places to just cremate multiple pets and then dole out ashes to various containers, so they started videoing the entire process for each person so they could be assured they were getting their own pets ashes.

Seemed a little overboard to me, but I also didn't realize it was happening so often.

There are much more stringent policies in place for human cremation, including the use of identification disks that don't burn, etc. But, frankly, if someone wanted to, you could still end up with different or mixed remains, but I don't really see that being likely for human remains.

Sniff test

Equally relevant, how much of the ashes are filler? Incinerated human remains do not take up a whole lot of space, and some places will fill it out with wood ash.

You can't make sure.

You can only trust in logic: why would the crematorium mix them up? It makes no advantage for them, but some risk in case the public finds out.

Why are you keeping dead bodies in your house, ashes or not.

"These other guys did it,"

Pretty sure there’s going to be tight controls and a state licensing board (at least in the US can’t speak for other countries) that set standards and codes for the handling of remains to when they are returned to the family.

Yeah just checked for the state I’m in lots of licenses and regulations. But I guess there’s nothing stopping in unscrupulous funeral home from just giving ashes of anyone or anything, but pretty sure if you’re caught doing something like that you go to prison for fraud and miss handling of human remains.

You need a control sample, taken while the person is still alive. Get them to chop off a finger or something, and burn it, and compare the two when the time comes. *

*The advice given in this post is not legally binding and is for entertainment purposes only. I am not a professional in any field relevant to the question. Conditions apply.