uhhh... aren't providers simply a subset of the female population at large?
i'm quite sure that there are civilian ladies out there who do not enjoy being fingered.
just sayin'... (yes, i am being ever so slightly cheeky here.)
to echo the statements of many others; it is all about the approach. when approached subtly and sensuously, i actually prefer manual stimulation to DATY -- mainly because when a gentleman is stimulating me manually, i can still kiss him and feel his body close to mine. i enjoy DATY just fine, but it gets lonely for me with nobody to kiss, and after being pressed close to someone for some time, it can get a little chilly too when that warmth is withdrawn...
i'm not going to go into great gobs of detail as this has been expounded on plenty so far; but a slow and gentle approach with lots of sensual teasing beforehand is, of course, best. and of course, all the bits about hygiene are crucial to an enjoyable manual experience... WASH YOUR HANDS WHEN YOU ARRIVE!, trim your nails, etc. etc.
that said, some girls may never enjoy manual stimulation despite the nature of your approach. and that's cool. it's simply a matter of figuring out what they DO enjoy. stimulation does not necessarily have to be directly sexual to bring pleasure.