It actually depends on the situation, If it's fake MacBook it could be running Windows, not OS for various things:
1. If it's just overheating, Your MacBook might be Core2Duo or the Fan is just dirty.
2. If it's running slow, it could be HDD Problem where Most HDD from 2008 to 2010 hangs a lot. SSD is power efficiency.
3. Most 2007-2010 they are Core2Duo unlike i3, i5 and i7 they use less power. Core2Duo in 2017 is still bearable when browsing the internet, but sometimes Gaming and Editing can be a problem.
My advice is i wouldn't buy a MacBook older than 2011...
If your MacBook is Fake It should be running WINDOWS XP 7/8/10 not APPLE OS Snow leopard, or whatsoever version..
If your Macbook is slow you can always upgrade it's RAM and Hard Disk Drive to Solid State Drive for faster startup and boot up.