Just dug up the old rating system I devised for walkups some years ago as mentioned by Kojac. I'll leave it to the new generation of Soho mongers to decide whether it's still of any use.
A = provides all services promised with a smile, generosity with the clock and sometimes a little extra

B = provides all services promised cheerfully to a good standard, resulting in you walking out with a smile
C = provides all services to a decent standard but you're generally reminded in various ways that this is a commercial transaction
D = provides most services but may exude some faint condescension or hostility and may for example charge for taking bra off or similar
E = basically pretty much a rip off with ill concealed hostility and poor service
F = fucking mental
Traditionally some reviewers would modify these grades with +/-.