For me, mainly I ask questions to inquire about a product, or a price, but that doesn't mean I'm committing to buy from the seller. Sometimes after inquiring I'd just stop and decide to not buy- but it's all usually due to financial reasons. I admit sometimes I don't PM them back to say I don't think I can get whatever it is that I'm inquiring about, and that's my mistake. But then, it's all part of business, as a seller or buyer.

Simple solution, just request for deposit for CODs to prevent FFKing like Doomsday said.