Well I once met a girl while visiting a trusted friend's town, I'd chatted with her for a while and she seemed nice enough, so before I left I added her on Animal Crossing. A few weeks went by, but I didn't hear anything from her so I'd forgotten about her by the time she visited. I'd opened the gate for somebody else that was visiting, and then she came in while the gate was open. I only had about 9 hybrids at the time, 2 or 3 blue pansies, a few pink tulips and some orange pansies, so I was a bit nervous that I might lose the few hybrids and have to start breeding all over again. Anyway, she went quiet for several minutes, I ran up to where I was growing the hybrids were and I could have sworn that one or two pansies were gone so I asked where she was, she just said "bye" so I flicked my switch off. I reopen the gates again and she comes back, I challenge her on her stealing the flowers, but she denies it so I give her the benefit of the doubt and let her stay, a few minutes later the flowers are gone again, and the moment I see they're gone the banner flashes across "looks like someone is leaving" so again I flick my switch off.
I open the gates again for the third time, and amazingly she has the nerve to turn up again. This time she stands by the station while I challenge her again, she doesn't deny it this time and just repeatedly says "im sorry

". I have in the back of my mind that surely she won't try it again, after having been caught out twice, but to be on the safe side I follow her round at a distance and I see her picking up the flowers, so I shout at her again while she runs to the station, and I switch off...
I still have her on my "friend list", I have no idea what her Mii name is or whether she's actually on my 3DS friend list or just on my AC friend list since I added her through AC rather than registering her friend code. She hasn't visited since that incident though, and I'm much more wary about adding people I don't know now.