What kind of interactions do you have that make this a frequently applicable concept? The only reason to get a good or service from a friend rather than a stranger professional is if it is in some way more efficient. Even disregarding the fact that asking for things from friends is generally less efficient because of the potentially fraughtness, this doesn't happen much for me. If I ask a friend to make me a cake, it's because I already know it is positive sum. If I want cake qua cake I go to a cake shop. The only examples I can think of where it would be applicable are:

• Staying with a friend for a period where it's unclear if/how much rent you should pay
• Division of chores with housemates (but limited applicability because IME people are averse to significantly uneven splits of labour even if compensated)
• Possible-example: in my world it is customary to attempt to offer compensation if you freeride on someone driving somewhere. I suspect this might seem strange to you, since assuming they enjoy your company and the difference in gas costs is negligible, the cost to the driver is surely negative so the money should flow the other way.
• Non-example: selling something second-hand to a friend - I would just use ebay price minus P&P, possibly with some arbitrary discount

This does not seem like enough to warrant minting a general concept, so I'm curious what examples you have in mind.

I think it depends on the accent. There are plenty of high status/upper class people with national (Scottish, Welsh, Irish) or London/West Country accents -- even pretty thick ones. On the other hand, a heavy Northern/Midlands accent is pretty indicative of a lower class background.