In English we have a very specific colloquialism/idiom to indicate our doubt in someone's premise. For example:
- Joe: Wow, you've really lost weight!
- Fred (who doesn't feel that way): If you say so.
- Mary: I love Tom. He's so loyal and devoted to me.
- Sarah (who saw Tom last night flirting with Jane): If you say so.
In English, the much stronger contradictory expressions like "are you kidding me?" or "you're crazy" almost demands a response from the other person to defend the truthfulness of their premise. But "if you say so" is gentler. Is there a German phrase that rides that edge of not outright disagreeing with someone in a confrontational manner, but definitely lets them know that you are not really convinced that their premise is valid? In other words, a common expression of implied skepticism?