If you charge say .30 per sq ft to clean, charge .32 or .34 sq ft to vac and clean. I used to just let my customers know that the carpet will need to be vacuumed before I clean and if they couldn't do it I would be happy to do it, but there may be a small charge for it.
I don't do that anymore, but it worked very well for me when I did.
I've tried breaking it down, I think it would come out to more like 15cents/sf, 40 cents HWE.
I've always included it in the price.
I get so much more out than the custy, even if they have a decent vacuum. $15/room isn't unreasonable per 100sf.
for my apartments if i have to vac i charge $25 and for most work i do thats my price for vacuuming unless its a very large home or office then i just pull numbers out my ass depending how bad it is and how long i think it will take.