Not quite the answers I was expecting, but interesting!
The Evans headset quote, I think they got wrong but for the record it was just for fitting one I provided and I think they have every right to charge properly, but it was too much. In the end I took it to my LBS which was (strangely!) less convenient and I trust them more! And cheaper. And they were amused to see a 14 year old frame!
Getting a bike serviced in London is a nightmare, especially since the increase in cycling. There are so many people happy to pay Â£10 + parts to have a puncture repaired. I don't say this as someone who often gets things done in bike shops, but from friends who offer to pay me to fix their bike - like the guy who spent Â£60 on a GT Palomino (in full Police paint job!) a year or so ago, took it to the bike shop and was quoted Â£190 to service it (including replacing a few bits)
I wondered what I should charge them. I'm happy to do favours for friends, but at the same time they want to pay me and it's a good excuse to use the cash on bike bits ...
[Caveat: I'm a rampant capitalist by trade. Everything has its price: the one the market will bear]