In this instance, their knowledge is worthless. Literally. You can get the exact same service for free, and that's what we're comparing against. If your friend doesn't have the requisite computer skills or the requisite reading comprehension skills to do his own simple tax return, then their service is worth it for him. For the rest of us, it is not worth it, and they advertise their services as if laymen couldn't do it as well. (When, in fact, I'm sure, they hire laymen during tax season to do all the simple returns and give them virtually no training.)

In addition, again, I'm sure it's not as if they give you the completed forms after you tell them that you're not happy with the service. The only knowledge you've gained is the amount of taxes that you'd pay if you used their service. You cannot provide them information that you don't bring with you, and they tell you everything to bring with you anyway, so it's not even as if you're getting the knowledge of a document that might be useful.

And your argument about the contract is specious. Part of their contract is that if you're not satisfied, you don't pay. I don't see how you can argue that exercising a provision of their contract is in violation of their contract.

I'd argue what they provide is a crap-ass job. And if you don't know that going into the situation, I still think it's perfectly reasonable to be unsatisfied with the result. If you do know that going in, and you still go in, that money would be better spent at a psychiatrist's office anyway.