@justoneofthosedays,
There are so many Lego compatible and knockoff or counterfeit minifigs out there that identifying those could take years and cost millions of lives. Just kidding but it would be quiet a task.
All you need to know if you intend to list them is if they are real Lego, by looking for their script logo, or compatible by trying to connect them to some blocks. The link below may give yo some helpful information or at least let you know how to list them. They may not be worth listing, if they are non compatible or unbranded knockoffs.
https://en.wikipedia.org/wiki/Lego_minifigure
"THERE IS NO SUCH THING AS FOOLPROOF, BECAUSE FOOLS ARE SO DARNED INGENIOUS!" (unknown)