The vast majrity of my work is within my town (Lutterworth in SW Leicestershire). I see my customers about town all the time and I am recognised frequently.
Now, I've been in this situation many times and like others here i will usually take £10 cash for such a job within town, more if I've had to travel.
i agree that many old folks are too proud to allow you to do stuff for free. It's also not fair on you, at the very least it's cost you some diesel and wear & tear on your van and tools.
I fully agree that if you treat your client fairly (both in monetry and psychological terms), they will do the same for you. When son or daughter wants a tub or bathroom or extension, Mum & Dad are going to suggest 'that nice man who fixed my switch for me'.
i admit that I do alter my 'charge' a little if it's obvious the client has lots or little money.
Many clients, but old folk especially, are woried about overcharging cowboys. Oldies will often fret and worry over the smallest things because they are afraid to call someone in case they get ripped off. Such is the power of 'negative telly'. So when you come along, do a decent job for a reasonable fee, you will find yourself in demand. It can be a bit of a pain going to lots of oldies with piddly little jobs, but look at it as advertising - it's getting your name about and improving your local reputation.
What goes around comes around and it will pay back one day. I've been very lucky and my payback has come round quite quickly. I've done lots of little jobs for oldies on a small private retirement estate nearby. The street light system needed work because it was badly wired and was tripping the MCB due to water ingress and corrosion. I've been commissioned to refurb all the light units and connection points. It'll be about £6k worth of work - I'm about two thirds the way through. When i'm there, the folks all say hello and bring me cuppas and biscuits. Top stuff.