Prices of things always go up over time.

As a seller, price the games right and they will sell.

As a buyer, pay for what you feel is reasonable or wait for the next one.

Why is this so complicated?

There are also seasonal peaks and valleys in pinball sales:

There are typically a lot of buyers around winter/Christmas time. Some people want projects and some are buying gifts for themselves.

Around the coldest part of winter and early in the year, buying slows way down. People have spent their money over the holidays and tend to take a little break.

When spring and early summer comes, sales get hot again. Summer projects for some, filling arcades and changing lineups for others.

At the end of summer and early fall (like right now), they tend to slow down again. People are completing projects, some are prepping for the holidays, etc.

This happens EVERY year.

It obviously isn't inclusive to everyone, but it is enough of a trend to be quite noticeable.

People also use emulators (like raspberry pi) on arcades. It has not only replaced done people searching for rare and/or expensive arcades, but it had also replaced a lot of people buying several arcades...since they can have it all in one. They tried it with virtual pinball, but it is no where near the same.