walk with them through the application and let them explain why they've built it that way, maybe with a 3rd party designer whom you trust ? so all of you can learn and it can be done in a mediating manor ?
don't know how much they've done, but i try to do it that way, because I tend to have a strong opinion on things so I need to be forced to listen so i can really understand why someone did something before jumping to conclusions.
just a thought. Maybe others have more experience :D .... invite mev and marco and sai and others ! :)