C. Charles Hahn said:
This seems like more of a "consumer psychology" question.... will customers respond better to a "chemical cost/usage" charge, or an "excessive stain" or "severe odor removal" up-charge?
With regard to a "chemical cost/usage" charge some consumers may respond negatively on the basis that "chemical usage is a cost of doing business for the operator and should be figured into their standard rate." On the other hand, it could be framed in a similar fashion to quick-lube and oil change businesses where the standard rate includes 5 quarts of oil, and those vehicles requiring 6 or more quarts are given a surcharge to account for the additional capacity.
An "excessive stain/severe odor" charge would alleviate the concerns of those who don't like a 'chemical' charge, by framing the situation as also including the fact that such issues are often more labor intensive to deal with than a standard service would be. On the other hand, some customers may not like the characterization of the issue in their vehicle as "excessive" or "severe" and may wish to argue the point with the operator that they do not deserve to be up-charged -- either because they are money conscious, or (more likely) they are embarrassed by the situation.
I'd say it's a crap shoot which way to go if you're setting a pricing structure that way, as you'll get positive and negative reactions in either case. Regardless, it is common sense to charge more when additional labor and/or product is required to do a particular job. Otherwise you risk losing money in the long run.