Is this worth it? Front Bumper
 

Wondering if this is worth the 100 dollars, or if its going to cause more trouble than anything. Not sure if this matters but he claims it was apparently already installed on an 8. Would that mean less body shop work to fit it on mine?

Rx-8 front bumper body kit - Mississauga / Peel Region Auto Body Parts For Sale - Kijiji Mississauga / Peel Region Canada.

In the add, he states that his buddy never installed it. And it doesn't appear to have been fitted (judging by the pics). I'd be wary...

Yeah, after speaking back and forth he mentioned his buddy had purchased it off of someone who had it installed.

No harm in checking it out, if it's local. If you notice that work has been performed on it, then the seller is probably true.
But, don't be surprised if it doesn't fit well. Be prepared to have some more work done to make it fit your car. Call around your local shops to check for prices