Adam is the owner of the store. It is Maitland's store, and he is Adam Maitland. Kinda hard to steal from yourself. Pay attention in the beginning. And it seems you are pulling these from the NitPicker's website.
Been there, seen 'em all.
Yeah, I guess you aren't a real fan of the movie. Any idiot would know that the store had a big sign that said MAITLAND on it and would have caught Beetlejuice saying that the Maitlands had died. Hey everyone makes mistakes, some are more stupid than others.