Quoted from RetroToys:There’s one on eBay for almost 4K and it’s not a prototype. Still available.
Ebay prices aren't real. Look at actual sold listings instead. Anybody can put any price they want on a listing--it doesn't mean they will get it.
Quoted from RetroToys:Still availabile
https://pinside.com/pinball/forum/topic/for-sale-police-force-prototype/
Most games, when priced right, usually sell pretty quickly. Holding to the same price for a long period of time with no serious buyers should indicate that something is amiss.
Quoted from RetroToys:3k isn’t much more than 2k, it’s negotiable ... unless you are just price policing something that’s never come up for sale before
It's true that it's hard to put a price on something special that hasn't surfaced before. I've gone through that with a few games I've sold. Basically, you have to try to find something reasonable comparable and start there, and then jump at a good offer or slowly lower the price until someone considers it a good deal.
There is some mild interest in the game, and it is an interesting example, but the price people would be willing to pay and the price you want for it haven't intersected yet.
Have you thought about possible trades instead?