i want to buy an Alternator from this guy, but i dont want to get scamed. how can u test it out?

 

just take it to the local autozone or advance auto parts, they test batteries alternators and starters, or you can get a 12v bat and test the starter yourlself, but the alternator you have to take it somewhere or put it on a car to test it

 

If you don't trust the guy, then don't buy it. You get what you pay for.