Most of those small stones have condition issues that make them inexpensive. If the seller says they are good for razors, hopefully they are (they probably are).

If he came out with a 2kg stone that was perfectly square and cleanly cut and said it was a top class razor hone for $50, then I'd really worry about it.

Most of those are koppa or mostly used up, but they very well may be decent razor hones.

Before buying one, I'd look closely at shape and make sure none had cracks across the top, were too thin, too small or had odd voids under the stone surface.

Also, if you look at the weights, a lot of them are 300 grams or so, which means there really isn't much stone there.

A thin one that can be glued to a base but is otherwise regular might be a good way for someone to try jnats, but the trouble with jnats is that when you buy a small stone to try a type, there's no guarantee a big stone will be the same as your small stone.