The funny part of this is that you called the guy and told him that you had a higher offer and then got mad that he didn't want the item after that. I'm sure that he assumed that you were trying to screw him out of more money and that was why he gave the response he did. I would do the same thing.
As far as the part about you selling it to someone else, I'm up in the air on that one. You had someone pay you more money and you took it, but you also had some kind of agreement with the other guy. That is where it gets to be in the grey area. Yes it's a little crappy that you sold it to someone else after the agreement, but there aren't any guarantees laid out.
Yes, what you did could be considered a little shady but it's not the end of the world. I personally don't know what I would do, but most likely I would take the money from whoever had it. I've had too many problems with people who say that they are going to come get something or pay for something later and then don't.