There were two cases of Buy More shoplifters during the series, the first one appears in Chuck Versus the Helicopter.
Casey setting policy
In the opening scene of Chuck Versus the Helicopter, Casey, and Morgan are seen chasing a shoplifter through the parking lot outside of the Buy More, and Chuck is chasing them. Casey manages to tackle him, and Chuck leaps on Casey to stop him from doing any damage to the perpetrator, "Casey, Casey, Casey. No, no, no, no, no! No, no, no, no! It's just a video game, okay? Lives are not in danger, and the country is still safe!" Casey does no damage but hauls the kid back to the Buy More. He is clearly an old nemesis for Morgan, who taunts him as he is hauled away, "Oh, hey, dawg. Nice to see you again, pal. Huh? You're not so tough now, are you? Oh, you don't like that, huh?"
The second shoplifter appeared in Chuck Versus the Webisodes 1, whilst Casey is talking to the Instructional Video Director, explaining his "unofficial" policy that has helped him all but eliminate shoplifting from the Buy More. He points out the shoplifter, then to demonstrate his three strike policy, he hurls an apple and knocks out a Buy More shop lifter. He then leaves to deal with it as the Director asks if they got that on tape.