Heads up.....Do not deal with this guy

The guy was wrong to sell your stuff to somebody else period, end of story. He should have told the walk in customer he didn't have any and that he could get one for that guy in a week. If he wanted to call you and ask if you wanted to sell your part that was in his possession, then that would be another story. Making it right isn't just admitting to it, it would be giving you both parts at cost and an apology not a phone hung up on you.