I'm at £1.50 sq/m to retailers on new carpet sprayed in warehouse before fitting. I've been charging that for years so should really increase but its all part of the big picture i.e relationship , recommendations etc.
Mike
P.s was using nano for years, no problems but recently gone back to stainshield pro . More expensive but I guess its a confidence thing on my part. I do tweak the dilution ratio to suit though.