You had asked about what to check for, compression test, etc.
There is an excellent buying checklist on this site here http://www.mastercraft.com/teamtalk/...4&postcount=47
Obviously, in your (and my) area of the world a lake test is out of the question this time of year. If the boat is in heated storage running the engine is possible.
But if this isn't possible, I wouldn't let it deter you. I bought both of my previous boats in the dead of winter, one of them sight unseen (apart from getting many pictures from the owner.) In fact, I was able to use NOT being able to lake test to my advantage in terms of price negotiation.
Assuming you are able to view possible boats in your area, a careful visual inspection tells you alot, especially if you are purchasing from a private owner. Plain and simple -- has the boat been taken care of? Things like the cleanliness of the bilge speak volumes. Are their receipts and records of maintenance? Talk to the PO -- lots! You will get a sense of his knowledge about boats and boating, his level of commitment to maintenance, etc. If he doesn't know an oil filter from a sparkplug chances are he didn't do much maintenance. (Now, if there are records for complete dealer maintenance, that might be a good thing!) Plus good old fashioned conversation helps to assay whether or not you think the guy is trustworthy.
If you are purchasing from a dealer I would ask for some sort of warranty, even short term, at least until the boat is de-winterized and you have a chance to run it. But you will also likely pay more on a dealer purchase than privately on any comparable boat.
This is a great site -- lots of knowledge (and humor.) Welcome! And enjoy your hunt for your perfect boat.