Just do a float test and check the backing, BW are easily identified, i have cleaned loads without any problems at all using HWE. Make sure the fixings are secure if not sure get some carpet tacks and tack down every ft or so leaving the head slightly proud, so that when the carpet is dry the customer can pull them out with a pair of pliers, make sure you charge for the tacking down. i Charge £15 takes about 20 mins.
Mark