The hammer and trigger mate at the sear. If this section is worn on either part then the result is what you have. This normally occurs because someone who didn't know what they were doing tried to do a trigger job. It could occur from extensive use, but it's not as likely. People lie to pawnbrokers all the time to try to get a better deal and I doubt S&W will cover the work if they find that the gun has been tampered with.