Toaster

So I just got on the server, I was sitting waiting for a medic spot to open because that is what I like to do, and I just decided to join the civilian team. When I joined I had a message that said I was banned for duping, for one week. But I don't even know how to dupe. Like I kept buying medic cars because I thought you lose them when you leave, and yesterday I found out that they just go to the garage. So I sold them all. Is that a glitch or something?