To me that doesn't looks like a bad paint job. That looks like paint over the bonding paste agents they use in that part to seal gaps. Either they applied that paste in a sloppy fashion or is just how they do it on all M3s. Since its on both sides I would guess they see that as normal. I agree that is not nice but that's part of the sub par build refinement that Tesla is known for. Service could file that down and then paint over it through to satisfy you. They should have done that at the assembly line.