A minimum charge isnt call for bait and switch , it's simply needs to be the minimum your prepared to travel to do a small job for.if your happy to go out to a job and clean 1 room then think about all those types of job you have done,figure out an average and there you go. Mine is £45 ,which I'm happy to spend an hour at the job for including unloading and packing away that's an hour total no longer. If they have other areas I try and suggest my 3 rooms for £99 , usually the other two rooms take under an hour since all my gear is setup ready to go it's a case of a bit more water in the tank and a bit more pre spray mixed up.
Upholstery wise ,I think I'm just really slow- perhaps too thorough and certainly need to invest in a better tool, I aim for £75 for a 3 seater £60 for a 2 seater and £45 for arm chair but happy to discount if it's a simple job