I'm a Terrible Judge of Character

So I work at this big-box electronics store and we get new hires all the time. Last week, one guy came in who seemed super cool, charming, funny, always cracking jokes. He asked for my help right away to show him around and introduce him to people, so obviously I felt a kinship with someone who was eager to fit in. I totally thought he'd be the best coworker ever until Friday when another employee overheard him bragging about stealing from the cash register and reselling stuff on eBay. Turns out all those jokes were just trying to butter me up for free help, and now I feel like an idiot for being so trusting. It's like a lesson in never judging a book by its cover, except this guy was a complete jerk who deserved to get caught. Oh well, at least he's not around to take advantage of anyone anymore.