You really just don't know what your talking about, which is fine and all. It's four bolts for the compressor, not two and there are no parts that need to be replaced if the system is open. There are parts that shops will try to sell you so they can make extra money but rarely do they actually need to be replaced. The drier/accumulator is the most common one of these parts. People will tell you that the dessicant bag inside it soaks up moisture and needs to be replaced. What they don't tell you is that an extended amount of time on the vaccuum pump will cause any moisture to evaporate, leaving the bag good as new, providing that it isnt torn and there is no foreign contaminants in the system to plug it up, which neither of those will be issues if the system was working properly before it was opened.

I was certified in a/c over 13 years ago so I know what I'm talking about. I don't really care if you buy the car or not. I just don't know anyone that would base whether or not they buy a car that needs the engine replaced on the a/c being charged or not.