This piece of advice only applies if you choose to go on. The main risk here is having your client blame your work for the likely failure of the app, even with

This piece of advice only applies if you choose to go on. The main risk here is having your client blame your work for the likely failure of the app, even with no proper ground for that. Imagine that you propose some design improvement over his specifications, this could be (from his point of view) the reason why the app is failing! So stick to specs, validate and transfer the responsability of every design choice to him.