"Trust me, I'm a designer" can be a very reassuring thing for your client to hear. But really, it's all in the face. A designer is visual by nature, so rather than verbalising opinions or recommendations, it will often just suddenly appear on their face. They'll get a confused look in return and possibly a request to clarify their expression. The designer may feel judged but generally, the client just assumes its a quirky way of being.... well just being. A state that is accepted in another realm but not totally understood in this one.
Here are some faces we've all made. Maybe not in person but definitely in response to a comment on the phone. There are some things that non-designers don't get. And that’s OK! But please trust us when we tell you that using Comic Sans is visual suicide, that a pixelated logo is not OK and that it’s generally not a good idea to edit anything in paint.
And one thing to note that applies to any job out there, it almost never takes 5 minutes.