I read an article once about how to find the difference between real and "just looking buyers. Basically it said to make the buyer give you something. if they are not willing to provide to full buying specifications or they say "send me what you have" than they are not serious.
I work with Fake buyers everyday and I say 2 thing to them every time. 1. that this is a 2-way street. 2. I can provide to you what you want if i dont know exactly what you need.