LPT: Don't ask someone to do a work for free just because you know them, instead, ask them how much would them charge you for doing it.

If they end up saying that they will do it for free, that's great!
Don't be sassy expecting people to do something they learned for free.

Example (This one is pretty common):
Steve is a Computer Engineer and you've known him for some time. He knows a lot about computers, but you don't and you need help to build up a PC.
Instead of asking:
Hey Steve, could you build me up a computer?
Ask:
Hey Steve, how much would you charge for helping me build a computer?
They will be more grateful knowing that you appreciate their work and time.