A pro would be when a seller calls it a cheap material but it is actually a very nice glass trade bead or good quality stone. If it's something I want I'll buy it without saying anything, then look at the rest of their items... just like going to a swap meet!

Sometimes I'll inform them of mistakes when I'm searching, but I try not to dispense bad news too often. Just today I told a seller their amethyst beads were garnet... not sure if that's better or worse, just different.

There is a seller who keeps trying to sell plastic beads as Venetian glass. Twice my messages have been rebuffed, each sent a year apart. Usually the response is more positive to such messages, but this guy just won't admit he is wrong.

Cons... most of the time there are not many as long as I trust my own research and knowledge and don't depend on what a seller has to say. I can usually return mistakes if they were purchased on Ebay... not necessarily so on other venues.

An Ebay education about collectibles has drawbacks. When I tried to learn about vintage glassware on Ebay there is as much mis-information as there is in the bead category. I now go to Facebook groups to learn things, or other internet groups such as this one. And books, of course.