I am noticing a few sell-offs lately, restored machines with a (hoped for) premium price,as well as a warehouse sale (Southern US).A lot more woodrails in nice condition, a few more 300 dollar "Specials" you didn't see 5 Months ago are showing up for sale.
Are the collectors selling off some stock? Could be. Deceased Owners collections being quietly liquidated? Not sure. I do know the customer is better educated as to the fun factor as well as value of EM Pinball, especially from places like Pinside.
I expect a slow to medium trickle of desirable machines to continue to hit the Market at realistic prices. I also see a struggle to maintain speculative prices on Sites like E-Bay.
Like any Antique the hours ( and parts price) necessary to restore one to working condition plays a part,as does the amount of climate-controlled room available.
The Buyers for these machines is shrinking if dependent upon younger people. They love to play them but do not want to invest the time necessary to learn parts numbers or techniques for repair.