I'm from a console video game collector background like NES and SNES. People have been saying for years wait for the correction. Wait for the correction. And what happened? Games continued to rise and rise and absolutely exploded last year. Will it correct? I guess that depends on your idea of correcting. Prices will go up and down yes, in 10 years will MM be a $5K game or a $30K game? My bet is on the latter.
We are dealing with known quantities for the most part. Supply and Demand. Your days of the A list going for cheap are gone. Sure you'll have your finds here and there but for the most part you're paying a LOT of money to own anything on the A or B list. We are in the time of technology. A simple internet search or eBay search will give even the clueless sellers firepower to ask market value for their pins.
I'd compare MM to something like Earthbound for SNES. Maybe not an ideal comparison but there are similarities. They are both considered extremely fun, have replay ability and everyone who is in that hobby knows what it is. Neither are considered "rare" yet they sell for top dollar over and over again. You could buy a NIB Earthbound for $10 twenty years ago and now? A NIB sells for over $2K. The cart alone sells for over $100 and there are hundreds of thousands out there.
My long winded point is... the secret is out folks pinball is freaking awesome and prices are on the rise. Those of us who grew up playing pinball hours and hours on end at the local arcade are starting to have the means to buy these. Expect prices to keep rising as supply dwindles.
P.S. A market correction is generally a 10% loss in a relatively short time frame. Take you avg MM price per Boston Pinball Pricing:
YTD $12,293
-10% = $11,063.70
Good luck scooping MM's up at that price.
What you are looking for is a Pinball Market Crash. That's not going to happen, sorry folks