Pros - whether on line or in person at stores/shows.....if the seller cares and is not so arrogant as to think they know everything there is to know about their item, they have learned something, and hopefully are willing to share it.

Cons - if the seller doesn't care or if their intent is simply to scam, I've wasted my time. But usually I can evaluate quickly - whether my effort is worthwhile. So the only "con" I can think of is the lack of satisfaction if my info is unappreciated.