How to check transmission?

I may have found a donor bike to fix my 2nd gear issues. I was thinking along the lines of a motor swap. I have e-mailed the guy a few times now, and he will be taking some pictures for me. He has told me the bike is is a non-running condition.

How do I determine if the transmission is any good, if the bike is not running? Do I have to take the chance, purchase the bike, get the engine to run and go from there?

 

First, you can attempt to turn the motor over and shift it by hand. Check the oil in the sump, metal particals/chunks in the oil mean bad things. Short of that, you have to pull the engine and split the case to determine condition on a non runner. Of course, it would be best to invest the time to getting it running first (unless you know the pistons have holes in them to begin with).
If the bike can be had cheap, you have a good chance at scoring a good engine.

 

Okay, this is where me being a totally rookie makes me look slightly retarded, but that is okay. Better to ask questions now then after I have seriously screwed something up, right?

How do I turn these motors over by hand? Where and how do I check the oil in the sump?

So far, the price this guy is asking is fairly reasonable, depending on the pictures he sends me. I might try to talk him down a bit, especially if the bike is not running.