you damn near gotta beat their ass once they start getting on that shyt, they're letting you know early you're about to get fukked over.
next time bring a pocket knife and use it to point out whatever issues you're having. it doesn't need to be unfolded, but have your thumb at the ready and stare at their forearms when they talk.
that'll put his bytch ass on notice

don't fukk with me and don't even THINK about reaching for no tools if we get into it.
mechanics can't work on shyt without their forearms... they'll either come correct or ask you to leave