If there was no good answer, do nothing. Don't accept an answer until it gets a good answer or forever: whichever comes first.
If there was a good answer and you're just being too picky, lower your standards and pick the best one.
Under no circumstances choose a random answer (unless they're all good and equally so - highly unlikely unless they're all dupes in which case you should [I think] choose the first to avoid rewarding dupes).
Of course if it's not a good question, you could make it better. And don't forget about the bounty. Maybe you should provide a link to it for more information.
You could also try communicating to the answerers why their answers do not suffice. It could be that one of them will be willing to improve their answer to an acceptable level.