I've also had some bad experiences, but it's a lot better than when we lived in Brockley (was once refused a lift at 11pm when 8 months pregnant - great.). We find that asking for "Dulwich Village" rather than "Dulwich" seems to help a bit (random I know, given that the prime consideration would be distance / ability to get a fare back, as noted above). But re the "no tip" annotation on the receipt, some city firms ask for this sort of statement as confirmation that expenses being claimed don't include a tip amount (I have worked for firms whose policy is not to reimburse any tip component of the fare)