> ...awkward feeling of not being able to solve the problem and still charging something...

I think that can be addressed by setting the right expectations. A discussion with an expert doesn't have to end with "the answer" to be super helpful.

A lot of times people have just gone down the wrong path and need someone to get them going in the right direction or even just confirm that they're doing the right thing.

This requires a empathy from the provider and grit from the person seeking help. This kind of work is definitely not a "stackoverflow" kind of thing. It's also can't be about the money, because anyone with enough skill to help people out with dev problems is likely already well paid and doesn't really "need" to do it.

Well, on codementor you can give a refund. And that would erase the session (and the rating, if you received one) from your history. I think it's better than tipping. Tipping, at least to my European ears, sounds like this voluntary thing as opposed to paying for a service.

BTW, what happened to your service? Or, probably better to ask, how far did you get and why did it fail?