When conducting trades online what is the proper amount of time to give before you move in and try to get what is on the table?

Lets say Guy A has a knife that both Guy B and Guy C want. Guy B initiates a deal and for several days discuss what is on the table in between amasses a list of trade values and descriptions and getting pictures of all blades involved.....and after sending that out and not hearing anything back the following day resends the email. 4 days pass, Guy B not wanting to sound too eager or pressure/bother Guy A decides to call on the evening of day 4, only to find out Guy C called last night and got it in a deal on said knife. Upon the call from Guy B to Guy A, Guy B finds out that Guy A never got the value emails...neither time he sent it. Guy A assumed Guy B wasn't interested in the knife and Guy C got the knife. Guy C and Guy B have had deals in the past and are on good terms.....should Guy B ask Guy C to back out of the deal as it was a failure in communication that he didn't get the knife or should Guy B just leave it alone and wait for the next time. The knife is VERY uncommon and Rarely/NEVER come up on open trade.

This is of course a hypothetical situation and all GUY A,B, and C are all fiction....I just want the Packs thoughts on this.

Jason