Another thing thats needs to be addressed is how you notify the poster that you will buy their product.
I just recently posted 3 minutes after a thread started that I would buy their product.I had to leave so I posted for them to pm me their payment info.I came home and had 2 pm`s from the seller.One giving me his paypal and saying to hurry up and pay him so he can mark it sold then 2 hours later telling me not to send payment because someone else had contacted him first.
I have had about 4 deals on the wanted forsale section where I was the first person to post I would take it only to have the seller say it was already sold.
If your buying something you should have to post it on the thread not just pm the seller.
part of this goes to the sellers integrity,,,,,,that said though,,,,,I think posting something like "I'll take the cue for the listed price" is ok, and not considered a cheap bump,,,,,,some sellers have a fan club that always come around and remark on what a great deal their buddy is offering though.