I am in central PA also and here is my take on things. Buying & selling pinball machines shouldn't be done in the ice & snow and anyone with any common sense doesn't want to move these 300 pound beast on ice. In the Winter in the northern 1/2 of the US you just never know when that might occur so it is a PITA buying or selling because of that.
Also - anyone that knows anything about early pins with painted backglasses knows better than to move them from cold to hot or hot to cold. Way too risky with the chance of paint pealing or lifting on the backglass. So it is easier not dealing with that in cold weather.
With that said I am in the process of selling off 65 machines in less than 6 weeks and have found this to be a great time of the year to sell. I have over 1/2 spoken for from just a couple listings on the Pinside Marketplace and one machine listed on Craig's list. To keep from things getting totally crazy I have just been posting other machines at the bottom of those listing or in my forum comments about those machines. It is working great! Lots of people who have taken time to look at my couple machines and the comments are finding my other machines and machines are selling quicker than I can get them moved to the garage and checked. I am loving it.