I trust commercial transmission places about as far as I can throw my 420SEL. After that, I trust tire store chains about as far as I can throw my 300D. After them, I trust mechanics with a messy shop (stuff laying everywhere-nothing organized) about as far as I can throw my 280SE. Last but not least, I trust people selling stuff on TV about as far as I can throw my E420.
Reminds me of a sign I saw at a repair shop once...
it read: "In God we trust, all other pay cash"