Before Paul was saved, his name was Saul, and Saul was not known for being a light-footed person. As a young man, it interested him to watch a man by the name of Stephen being stoned to death. As he grew and was educated in Jewish law, he became a zealot, and with fierce passion, he persecuted Christians. Saul was making a name for himself. As always, in such a situation, there is much more assumed about a man than is actually true. No doubt Paul was charged with things of which he was not guilty, because of the way he had portrayed himself.
Interestingly, in Acts 9, Jesus had taken note of something in Saul that no one else seemed to notice. Jesus noticed that Saul was "kicking against the pricks" and that was not an enjoyable time for Saul. I would call this conviction. You see, beneath the surface of what appeared to be a hard, calloused man was a man in turmoil, with a desire to do right, but expressing it all the wrong ways.
In a way, I can relate to Saul. I too have had a desire to do right, yet have expressed myself in many wrong ways. I too have left impressions on people that have caused them to doubt my sincerity, as the disciples did with Saul after his conversion. I too struggle at times in the transition between who I've been and who I am, the impression I've left and the individual I've become.
There is really nothing you can do to change people's minds and force them to believe you. I've come to the conclusion that just like Saul/Paul, the only thing that you can do is live the difference. When people assume that you're spiteful...live the difference. When people assume you're angry...live the difference. When people assume you're retaliatory...live the difference.