Am i obliged to buy when seller refused at first..

Dougmc, no, when you click on the "make an offer" button through Audiogon, you are committed to buy for 48 hours, or until the seller declines or makes a counteroffer. Whichever happens first. If you back out, you are charged a $19 fee from Audiogon, and obviously, open to negative feedback.

As to Audiogon's reasoning for their rules, you would have to check with them. Yes, it does tie up the buyer. I think Audiogon wants to make sure buyers are committed to the purchase at the offer they are making an official offer. Trying to prevent buyers from just making official offers on a dozen objects, and just picking out what they really want later. Only Audiogon knows for sure.

Did you save that message the seller sent you refusing the offer?
If so, I would think that should be enough to have Audiogon have the negative
feedback removed. After all, he did not accept your offer and you're right to
move on.

What a joke A-gon has become. And that loser,cry baby
seller! What happened to FREE enterprise? I mean can't two
people negotiate without big brother standing over us and
watching every move? No wonder I've been gone a while.

IMHO AudiogoN got this wrong. If the seller failed to use the proper AudiogoN system procedure for declining your offer, the seller is at fault and you should not have been penalized.

Though there are two sides to this problem I can understand Veerapaneni’s position. It would seem that the seller, having sold his amp and knowing he declined the initial offer, should have not been vindictive. Sounds like a poor sport to me. I would contact AG and see what they can do.