I think it's a 2-way street that makes things get screwy on Audiogon...
For instance, a guy (Mr.1) offers me $300 for something I'm advertising at 450 OBO. Another guy (Mr.2) offers me 350. I'm a little suspicious of Mr.2 because of some mixed feedback/gut feeling etc. but, I tell him I'll take it. I tell Mr. 300 that I got an offer for 350 and that I'm selling it.... he says OK... but then, says, he'd like it for 375.
I feel better about dealing with Mr.1 and now he's offering me more money. It's the 'best offer'. So, now what? Stick to my word and deal with Mr. 2 (as I should) or, take the 375 and tell Mr. 2 he's been 'outbid' so-to-speak.
This happened to me and I had never been faced with it so, I didn't know what to do. As it ended up, things took care of themselves. Mr.1 backed out and I sold it to Mr.2 for 350. No big deal but, I did wonder for a little while as to what to do.
I'm not saying my situation is exactly like this one but, the guy has several positive comments and I'm trying to give him the benefit of the doubt. Maybe he was faced with a similar situation... maybe he simply didn't trust you.... Could there have been ambiguity in your phone conversation that led him to believe the deal wasn't 100%?
If it were me, I would have stuck to whatever we agreed upon. If I didn't like the deal, I would tell you why. As far as I'm concerned, if I believe you're sending the $ and we agree on it, it's a done deal in my book. But, if you left it up in the air a little on the phone and then asked for an email with details for the purchase, it's still not a done deal.... and may be what happened.
I don't know any more than what's in this thread and what's in that guy's feedback. So, take what I say with a grain of whatever. But, it looks to me like there was a misunderstanding and not malice.
-Carl