Wow, I just started reading this thread again. Crazy turn it took. It really sounds like your sister needs help, professional help. If she's stealing from her own brother thats a serious problem. But to steal, and sell something on Craigslist takes a special kind of person. Honestly I understand you wanting to write her off, but that's really not going to change how she is. Most likely she will do it again. I would go to her very calm and concerned and try to get her some sort of help.