Are you looking to modify it afterwards or keep stock?

Get a pre purchase inspection done at a Subaru specialist like MMS or Stechnic and go from there.

If you plan on modifying the car afterwards it might be better to buy one with some of the basics like tune/exhaust,rims,swaybars etc already done to save some dollars.

An obvious thing to pay attention to will be the clutch take up point. It should be pretty close to the floor in that model. If its half way up the pedal travel or higher and shuddering it might indicate one that has been driven hard and put away wet regularly, and clutch may need replacing.

Listen to the engine during warm up, if it's loud and chattery like mine run like fuck!

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Bye bye betty blue. Hello F6.