Is there a way to filter out questions from users who don't accept answers? It seems like a great waste of my time if I'm not even sure they're going to come back.
I've never seen much point to this. If you're worried about reputation or badges, most of it comes from other people voting on your answer. If you just want to help somebody, as long as the question is initially well-thought you can do that regardless of whether they accept your answer or even provide additional feedback.
Don't forget though that you're not just helping the OP, you're also helping those who come after with the same (or very similar) problem and have found the question through Google.
You never know, they might just give you an up-vote for your efforts.
I am concerned because what happens when you ask a question, meaningful people put a lot of effort into answering the question, but ultimately none of the answers is valid. I would love to give a "great effort" to the person who put in the most work, but I cannot accept an answer which does not solve the question correctly.