False Chargebacks - Fraud for Sellers
This is something you must always be ready for as a seller on eBay. This is really the main eBay payal scam too. Buyers can easily claim that an item was damaged in shipping, or that it never arrived. They'll then walk away with a free item, while you're stuck with shipping fees and a refund.
For the prevention side, make sure that you enable eBay's filtering. It just makes sense to filter out buyers without verification or with negative reputation. Even if you know better than to send an item to a scammer, they can still run up the bid (since they don't plan to pay for it anyway) and force you to relist the item at your own cost.
Make sure that you get delivery confirmation for all purchases. A tracking number may not mean much, but it helps and it's usually cheap (or even free if you're buying your postage online). Anything remotely expensive needs insurance. This is just a good idea, since damage does sometimes occur and packages are legitimately lost. Only turn down insurance if you're okay with writing the item off as lost. Also, being able to rebuff claims of “damages" with, “fine, please file a report" is surprisingly effective.
You will also have to make judgement calls at times. Cheap items may not be worth the hassle. More expensive items that were “damaged" are certainly worth some pressure though. Pushing for a return of the damaged goods could be worth it.
Note that the worst option is that you'll be paid with a hacked account. If it's a legitimate hack, then there's just nothing that can be done. You'll have to pay a refund and that's that. False claims of unauthorized purchases also happen, and again, there's not much that can be done.
Overall, your best bet is to try and stick to eBay's seller protection plan. This is the one thing that all sellers using PayPal need to know. If you send a physical item to a verified address within 7 days of the purchase, and the item matches the description, then you will be protected against chargebacks. Delivery confirmation will work for items worth less than $250. You'll need signature confirmation for anything higher than that.
Sticking to a confirmed address is probably the most important step. This will protect you against unauthorized charges. They can't exactly claim that it was a hacker, if the item went to their billing address. They can verify their address by adding a credit card with that address to the account, or by following the alternative address verification that PayPal offers.