I forgot the very best sale (or "sale") I've ever done. 100 years ago, in a previous life, I needed an extra beater to drive, after turning my DD Miata into too much of a track car. I found a manual Nissan 200SX -86 (the squared 80s version with pop up headlights and a talking onboard computer) at an auction and got it for $500. It was mint, everything worked - Somebody had obviously loved it for many years. It ran flawlessly for over a year, despite me drifting it daily.
A friend had hit some financial trouble. She had a part time job at Lowes, but what she made barely covered the cost of daycare for her 6 year old daughter (whose father was MIA, of course). She considered moving back home to share a house with her sister and mother, many states away. One day, her car was repossessed at the daycare, while she was picking up her daughter. We guessed they couldn't get to the car at her apartment, so they followed her and took it there. She was now stuck with no car, not being able to get to or from work or daycare and of course no money or means to go home to her family. She asked if I would consider selling the old beater and get paid bit by bit over a couple of months...
I gave it a good service and sold her the car for $1. It didn't make a big difference to me, but it made a huge difference to her.