We strip and paint, and we paint over wallpaper (we always use oil primer).
Requests have been on the increase.
We've also had a few customers do their own stripping and had us skim.
We wipe walls after paper removal to get rid of paste but in most cases some skimming is required, so we generally sand any remaining roughness and prime with an oil primer (SW ProBlock).
After being burned on a couple of jobs, I do not quote a flat rate.
Don't ever assume anything about what you'll find.
One job: Multiple layers (the homeowner said there was only one).
One job: Wallpaper had been applied over bare new drywall, discovered the builder had not taped the corners of the drywall or applied finish skim coat to taped joints and nail heads. I'm seeing increasing numbers of newer homes (5-8 years old) where the builder installed paper over bare drywall.
One job: Wallpaper over plaster. Plaster fell apart, numerous heavy-duty cracks and detachments from lath. Found walls under wallpaper covered with black mold.
I've had a few prospective customers walk away because I wouldn't quote a flat rate. I don't care--I remind myself of past nightmares.
We don't use DIF--it doesn't seem any better than plain water, IMHO.
We perforate with a paper tiger, spray frequently with water, and let it soak...the more soak time, the better the removal.
99% want paint--no wallpaper.
(We're also getting increasing requests for popcorn ceiling removal.)