Apparently I'm not dishonest enough about my mistakes owing up to my mistakes too much when interacting customers. Fuck me for being honest, I guess?

Depends. Are you a freelancer? If so, it's healthy to learn a bit of salesman tactics.

Are you an employee? Why are you dealing with customers in the first place?

I am always honest. Haven't lied once for decades now. To anyone.

It's all in the words and angle you choose to present the unpleasant information in.

A key note about explaining technical mistakes is to a non technical person is not to take your technical background for granted. Imagine you have to educate them from nothing to your level to understand why that mistake was so obvious