Just to add to witcher_sense's good answer above: The methods aren't audited because their methods aren't even known. Most of these services will just take an address one of their paying customers feed them, and then return some breakdown of the percentage of coins from various places, such as centralized exchanges, DEXs, casinos, scams, etc., with absolutely no information about how they reached that conclusion, and then their customers will treat that as gospel. There's nothing stopping anyone from spinning up their own blockchain analysis service and charging extortionate rates to tell other people where you think coins have come from based on complete guesswork. And as we regularly see, they often get things wildly wrong.

There was a post I made a few months ago about how one such service shows that large amounts of coins in the hot wallet of large centralized exchanges are "tainted": https://bitcointalk.org/index.php?topic=5395035.msg59905002#msg59905002