I have a slight problem with the notion that an approved used car has to have perfect paint. It doesn’t - minor defects commensurate with the age of the vehicle are considered acceptable.
You are correct...Approved Used for Mercedes does not mean paint perfect and you won't find any dealership that will state that the used vehicle is paint perfect.
You need to go over the vehicle carefully, and bring the defects to the attention to the salesman. If he doesn't want tp play ball, talk to the branch manager and see what they are willing to do to rectify the issues you have spotted.