I don't see where the seller got out of line at all. It's his prerogative to not want to haggle over messages: put in an offer or not. He can accept or not. Questions about the item are fine, but to a point. 'sell me on this over the one at Guitar Center' seems a little much to ask over reverb messenger. Getting offended that the guy didn't want to deal with you anymore seems like the wrong response if you DO decide to haggle, since you always run the risk of ruining the sale or offending the seller.