Mark, do you clean much deep sculpted berber? Not just berber, but the real deep sculpted stuff. I have to deal with a lot of it, and if it has been badly neglected it is usually a nightmare. Pads skim over the top of the crevices. A carpet wand doesn't get maximum suction. The scrubber that I have doesn't have long enough bristles to dig the crud out. What do you suggest?
If you have any of the Fiber-plus pads from Excellent-Supply, you might try these. If you dare, you might even also try their Fiber-max scrubbing pads, but these are VERY aggressive. I suggest discussing matters first with the customers. Are their expectations realistic? Are they prepared to throw in the towel and tear this stuff out if it proves to be not-cleanable? Or if your scrubbing causes some difference in carpet appearance? You need to know when to hold them, and when to fold them in any business or endeavor.
use green striped or brown striped Tuways. they come in sizes to fit either your Challenger / OP or your Cimex.
if you want to remove more soil after that, try using a "loopy" all cotton bonnet. but the Tuways work for me. that colored strip can dig into the valleys nicely.