It's a symptom of a larger problem. You're probably dealing with kids that don't know how to interact with others on a professional basis. They're lazy, and only think of their own wants. Nobody's under obligation to buy after an inquiry, but they should at least write back to say they aren't interested if they change their mind. That just professional courtesy. As far as bumping a thread goes... It's nice to do, but not required. Inquiries that contain useful, non-sensitive information should be made in the open forum, and you'll then get the bump. Otherwise, I think it's the OP's job to maintain the thread.