The whole reason you hired a locksmith, was to fix a problem with a lock and/or key. You hired someone who could theoretically do the job, afterall, that's what they do, and that's why you hired them.

If he came out and made it worse, then he should fix it or pay for it. Even if he has to pay for it, he's keeping the customer happy, and he's taken a learning "seminar", paid for by him. Afterall, if he's not paying for a problem he created, then he was put in a no lose situation; fix it you get paid, break it you walk away scot free. That's a pretty good deal, and not how business typically goes.

Seems to me the locksmith should take it on the chin. He can now use this experience and learning about a vibrating sander now to fix other cars.