For me "old school" means that a Mistress is professional and well-trained, with plenty of safety protocols, respects her clients and has a great reputation.

"Old school" also means, at least for me, an independent Mistress with her own playspace or one who may own a dungeon. The Mistress is only into BDSM. She certainly doesn't cross into illegal activities. As someone who began in the '70s and returned in the '80s, "old school" is a fine compliment.