I just tell them why it’s a bad idea to their face. Some appreciate it, and others just find someone else to pitch their ideas to

One client has a whole solution from me and occasionally keeps asking for this or that thing and I have to tell him what part of the app already does that because he can’t keep track of all the things he’s asked for already.

If I had the time, I’d use the benefit of hindsight to restructure the whole thing and hope it’d help his pea brain along, but as it is, I spent too long just adding features wherever he asked me to, without taking the time to question whether that makes sense.