Very good advice - but I think it applies more to rotaries than the PC. The PC is a different type of machine than most shops use - it's a random orbit polisher, so as I am sure you know it's designed to be a lot less aggressive than a sit and spin rotary - it also spins about 1/4th-1/8th the max speed of a rotary. Shops use rotaries because you can take out much worse marring with them, and much faster - PCs are designed more for amateur weekend warrior type applications. Regardless to say it is much more difficult to damage paint with a RO than a regular rotary.

Cheers.