I would scrap the Ebay option. If you sell it or do not sell it on Ebay you still pay $ to list the car.
I would stick to Auto Trader and state specifically the price you want is FIRM. Otherwise you open ourself up to be haggled before and after the test drive.
Perhaps you can request to see a letter of Loan Pre-Approval. I was given one from my bank before I bought my car that let me know how much I could finance.
Being a member of PCA definitely narrows the potential test drive, however you potential buyers will be from all walks of life.
Being 26 at the time when I bought my 986 S, I narrowed it down to 2 vehicles, one from a private party and the other from an Audi dealership. After I paid $180 (each) for a PPI I ended up going with the Boxster S from the Audi dealership (same price) because the Private party vehicle had an RMS Leak that needed to be fixed, AGAIN, which was within the 2/24000 warranty.
Just my experience, hope it helps.
KRZ