I don't think I'd blame you, you really don't know how well or not he was taken care of before you got him. A normal, healthy veiled should be able to handle a stressful day without toppling over. Otherwise no one would be able to take their chameleons to reptile shows for the weekend, sell them, have them go home with new owners without all of them dying.
Whatever you choose to do next, I'd look into ordering from one of the forum sponsors. They have great reputations and take great care of their animals, so they guarantee that you'll get a happy, healthy guy.