John,
The face fibre on a BW is polyprop so if you do a float test and the fibre floats, then lift the carpet in 1 corner and inspect the backing.
The weft shots on BW run in both directions crossing each other.
BW used to stand out like a sore thumb with bold pattern but these days they can be plain, however i believe that the newer versions are not as prone to shrinkage as the older ones.
you may have already cleaned one without even knowing, dont be scared by them, i have cleaned loads that other cleaners have run a mile from and never had any probs, check all fixings and if not sure you can get carpet tacks and tack every foot or so leaving the head proud so that the customer can pull out once dried.
Mark