I am buying a used Evo within the next two weeks... is there anyway to tell if the previous owner used regular gas instead of the premium?

 

Not to my knowledge. Best to just fill with premium and clean the fuel systems.

 

What makes you think they did?

 

No way to tell, just inspect the car close and make good choice!

 

If you are that concerned about it, I would bring from fuel additives with you and dump it in the tank and fill it up with premium gas.

 

If they used regular gas they would have hella knocking and have done significant damage to the cylinders

 

Not necessarily. The stock ECU is very good at protecting a stock engine and will pull timing as needed. Running 87-octane would honestly probably do no damage to a stock engine and would just result in lower power output.