I've read a few threads about people buy "unmarried" AP's only to find that they were not really unmarried. It is kind of a risk; you could end up spending more than a new one after buying it used and having Cobb fix it. If it's on ebay, check the seller's feedback percentage and also the number of transactions.
Or, you could try to find one locally so you can check it before you hand over your cash.
Good luck, you will love Stage 2.