I was just wondering if there were brands that you would never buy from and the reason behind that (bad customer service, poor quality, etc).

For me, it would be Vintage VDB. The guy behind the company started out in the vintage Panerai rep game a number of years ago and sold his builds for big money passing parts off as things they were not (ie cases as perfect reps and movements as geniune Rolex 616s and 618s) even though they were not or were frequently poorly modified versions of cheap parts. So ignoring the replica thing, the fact that he passed things off as things they were not and scammed a number of people out of a lot of money makes me not want to have anything to do with Vintage VDB.