Testing Components

The same way you would test any other computer part, by sticking it in a known working computer and seeing if it still works.

Thank you for responding. I was trying to avoid removing the logic board or anything else if I could. If I did remove the board I would not have another system to try it in anyway. Is there any other way? Maybe with a voltage meter or something?

Nope, like all other computer main boards, the only real way to test them is to use them. If I were you, I'd just put the Macbook back together and plug in an external monitor and make sure that it works. Then I'd look into the price of a new LCD. The reason that they may of taken it completely apart is that on so Mac laptops, you have to in order to get at all the parts related to the LCD.

Thanks for the response. I tried to put it together and use an external monitor as you suggested. When I plug the power in the light on the adapter plug that connects to the computer turns on, but the computer still does not power up. I believe that he is telling the truth about it working before he took it apart, so it must be a problem on my end. I would really like to figure out how to verify which parts are good. My intention is to part them out and sell them on ebay. I have bought a total of eleven laptops from him and it seems that selling the laptops for parts can be very valuable. Any other suggestions would be greatly appreciated. Thank you in advance.

If there are any tools to test Mac parts, only Apple has them I'm afraid. The RAM, hard drives, and disk drives can all be tested by standard means, but for the rest I only know of using them for testing.
If you are going to part it, you'll just have to list them as untested/as-is.