I had one guy ghost me after accepting one of my offers. He never paid. But it worked out in my favor -- after 24 hours I got to split his bond with the operator, so the "bad guy" lost money and I gained it! That was the only time someone has tried to do anything malicious to me. But other people have had bad experiences, e.g. see this reddit thread: https://www.reddit.com/r/robosats/comments/1e4r106/i_was_scammed/