Conrad,
I would not slap your wrists , constructive sharing of info is what the forums are about.
One way of spotting a BW is that you can see the pattern from the backing.
Another is the harsh feel ,( polypropylene ) if you rub your knuckles vigourously on a BW they will become hot and sore due to the friction.
A real wool Wilton has a nice soft feel.
Another is to burn a loose fibre , it will melt if its PP and form a black globule.
And last but not least is the flotation test, a PP fibre will float in water even if you wet it out , whereas a wool one will sink if wetted.
Cheers,
Doug