Steve O., The others have given good advice on approaching a seller via a polite inquiry into whether a particular knife is still available as a "For Sale" or as a "Trade" item. Courtesy is the operative keyword, which if followed should stand you in good stead with any of the many knife knuts I've known and dealt with in the past.
1whobuys said:
what do you guys think of someone taking a deal and then just turning around and saying " Sorry, I'm not selling after telling you I would?"
The exchange of emails (or verbal agreement) confirming the sale is a contract in the strict sense of the word. Beyond that, in the online knife knut world, a person's reputation for integrity is made (or broken) on how well and consistently they follow through on their word.
I have had many knifes I have sold and regretted before they left the house, but I had given my word on a deal so they went to the new owner.
+1,000 to that amigo! Seller's regret can strike deep in the soul of Bussekin sellers. I know!!

But once the word has been spoken at the Trough, the deal has to walk IMHO. That deal ain't got no reverse gear at my end. Of course, that may well put me on the hunt for that exact same knife again immediately or later on, but that's a consideration outside the original sale.
ALSO, what if you contact someone about a knife and they don't answer you..?
I give them the benefit of a doubt and figure they're swamped with life issues & don't have time to get a reply out. Especially if the deal is very good price and the listing more than a couple weeks ago, since those tend to go quickly. However, I've also sent a follow-up email or two seeking status of the knife, if it's a knife I'm particularly interested in acquiring.