"Rule of three" of the hobby I have used for three decades and it works:

1 ) Know your local "flippers" and don't sell to them. It's like a disease, and spreads like a virus. It is 10x worse than it was 10 years ago for example.

2 ) Sell to networked friends that you know will take care of the games for the right reasons. It keeps your games from showing up on Ebay or Craigslist the next day. Sometimes the whole experience can be a circle, and tue same games end up in your own hands again.

3 ) A game is sold at fair base value with considerations of restoration time and effort (if applicable), but not necessarily modifications. What this means is don't sell a game as "restored", if it still a "project".

The only thing that has changed is I don't give away project games anymore due to market stupidity. No more free rides to new enthusiasts. The ship left the harbor more than decade ago due to too many people that decided to take but never give anything back to the hobby. Those that have networks still use them with fairness.