I think the OP did the right thing (not using the ATM.) I carry at all times, too, so I think what I also would've done was just sit in my car and wait to see what he did next. I would've done this only because I would worry about the next person who came to the ATM. If he would've lingered too long or watched other ATM customers too intently, I would've called the cops. I understand that others may not have the time to take such an approach, but I sometimes do.