Pinkind has long debated the philosophical question; Which came first, a "people keep offering more money!" thread or a "are we in a price bubble?" thread.
The truth is, we may never know.
This has always happened in this and every other hobby. This has always happened in pinball and will always happen as long as there is a pinball hobby.There is nothing you can do about it.
Mark those sellers off your list and keep looking, eventually a deal will work out for you.