I'd just like to chip in that in my experience being cheap does not equal 'bad' punters - you get wankers at all wealth levels. It's more about how you market yourself and how you screen. If anything, going very high end my suspicion is you'd get more boundary pushers.
Totally agree with this. I have had clients at both ends of the spectrum: I've had high-ranking investment bank executives, and I've had the guy who pushes the trolleys back at Aldi. Arseholes occur at every income level!
To answer the original question, I adjust my rate according to my location, as I only tour. If I'm in the north, I am generally at 70/100/120, if I'm in the south then it's usually 80/120/140. In London it's 100/130/150.
The only time I offer a reduction on that is if I am giving reduced services, e.g. oral only bookings because my vagina is sore. In that case I'll generally offer "40/50 quid blow and go special" and when clients call I'll make sure they understand that it's oral and HR only.
BTW I am plus size and in my 40s (advertise as 30s LOL) and have no problem charging 100/150 in London. If you currently feel you are more curvy than slim, then advertise as such - lots of guys love curvy girls and you could tap a whole new market!