My wife calls me a "collector of collections." As such, I can tell you that you see this behavior in every type of collectible. The more access you have to a good quality or quantity of games (arcades, friends collection, your collection, shows, pinball leagues, etc), the easier they are to sell. Also, the less time and money you have into a game (sentimentality), the easier they are to sell.

I love all pinball machines, so I feel your pain of selling...but some are just better than others. If you have access to go play games at arcades, expos, friends homes...go play them. Build a "wishlist." Go find what your favorites are and those that didn't qualify become easy to sell.

Don't invest tons of time and money into them at the start. Once you do, they become more difficult to sell. Find out how they compare to other pins first.

Narrow your pinball search to begin with. Inevitably you will gravitate to certain things. It may be lighting, sounds, theme, ramps, etc. Once you find what you fancy, it becomes less of a chore to buy what you like...or to sell it if it doesn't meet your criteria.

Once you get a game..how much do you play it? If it is a few times a week, you should probably keep it. If you go weeks without and you don't miss it, it's time to move on.

Space restrictions. Only having so much space will help you make the tough decisions. It's much easier to sell pins when you can only have 3 as opposed to having room for 100.

Lastly, money decides a lot for you. Would you rather have a current pin or another at the same value? Would you rather have that pin or the money? These hard questions will unearth a lot of truths for you.

Access, sentimentality, time, space, and money ultimately dictate what comes and goes. You have to decide where your values lie for those.