A client hired you to specifically write an app in Ruby on Rails, and you decided to use something different?
I hope he is prepared for: 1) the possibility that the client will refuse to pay; or 2) sue him later, if he finds Sinatra cost more to maintain than RoR or finds he has to have it redeveloped because he really did need RoR.
Why even risk it? Why do you even care what language it is THAT much? It's not your project.
I can understand why you would care about what language it is. But there's nothing wrong with charging more to work in a language you dislike; you just have to be upfront about that.
You care about the language SO MUCH that you would be willing to risk developing the app for free, or worse free + real damages + punitive damages (for fraud)?
There's no language that I love so much that I would risk a lawsuit over it.
Of course not. I totally agree that you need to have client approval over what you end up using. But my point is that if the client wants you to use a language that takes you longer, or that you are miserable to use, you can reflect that in your quote.
I hope he is prepared for: 1) the possibility that the client will refuse to pay; or 2) sue him later, if he finds Sinatra cost more to maintain than RoR or finds he has to have it redeveloped because he really did need RoR.
Why even risk it? Why do you even care what language it is THAT much? It's not your project.