Hm, seems suspect to me. If the agent said there were no other offers, said he would tell you if any other offers came in. Then, another offer got accepted before you had a chance to revise, seems fishy to me. Clearly someone dropped the ball. Don't know who, but someone didn't communicate clearly about what the expectations are. One more example of why we need to have stuff in writing, even what the agents talk about. In my experience, that kind of thing is generally not a problem. Most agents do what they say they're going to do. I had the same experience last year with an agent that said they'd tell me about new offers coming in and did not do their job. It happens, but I'm not exactly sure what your recourse is.