Hello!
I purchased an item on eBay 8 months ago. I went to sell it and was told it is not authentic. I did not authentic it at the time.
Do I have any recourse?
I don't think so. It is too late for disputes through ebay, paypal, or your credit card. If you purchased it on ebay and it was removed on ebay, you can call ebay and tell them you bought it on ebay, so they will remove the defect from your account. You could try contacting the seller. If she is reputable, she might consider taking it back or giving a refund, but she is not obligated to do so.
I have a few comments.
No one knows whether the item is fake or not or if the listing may have been wrongly removed. Without intending to beat you up, when buying potentially faked items, you should have checked authenticity either before or after your purchase 8 months ago.
Before doing taking any action, my suggestion would be to post pictures of the item on the brand-appropriate "authenticate this" subforum here on TPF. I don't know what brand it was and some of the authenticators here don't authenticate completed listings, don't authenticate for sellers and don't authenticate without links to listings so you may be forced to invest $7.50-ish on a professional. But it doesn't hurt to post and try to get help here first.
If the item is deemed as authentic, you can submit an appeal with pro documentation to ebay. They should remove the ding and reinstate the listing.
If the item is deemed as fake, then the removal was appropriate and you'll be at the mercy of the seller. If she's honorable, she might be willing to issue a refund but she's under no obligation to do so at this late point.
And (assuming it is fake), if she's unwilling to refund, you probably have nothing to lose by trying to file a credit card dispute if it was paid that way. If you lose the c.c. dispute, you'll have to consider this the price you pay for not verifying at the time of purchase.
But again, first thing is to find out whether it's fake or not.