to be honest, I simply not sure what I ended up paying him in the end.

had him booked for 8 hours for Wall and Summer Palace (quick stop only - so included bringing back to hotel)

I ended up using him only for Mutianyu Wall trip only (less than 6 hours total)

Paid him either 550 RMB or 600 RMB (one of the two)
Basically, just paid him whatever he suggested as I was pretty happy with such stress-free trip (had heard too many ugly stories about tours with mandatory shopping stops and cheating taxi drivers)

Wall trip was the nice part of short Beijing stay.
The rest of BJ, I was not that impressed.
Particularly disgusted by what was going on in the evening/night at JW on executive floor (supposedly same floor where US secretary of state stays).But then others on FT hinted that it is not that unusual practice by some western vistors. oh well, i will remmeber the good part - nice hassle free wall trip and nice 2-3 hours on crowd-free wall (again Simon's suggestion to ignore chair-lift and instead take gondola and go LEFT was a useful one)