Watches and sneakers

eBay sends watches sold for $2,000 or more to an independent authenticator before they reach you, at no cost. Between $500 and $1,999.99 you can add the same check for a fee. Sneakers from top brands priced $75 or more are checked too. Look for the blue Authenticity Guarantee badge on the listing.

Every serious watch has a reference number on its papers and between the lugs. Search by it, as in the list above, so you compare the exact model, not a cousin with a different dial or bezel.

A watch with its original box, warranty card, and receipts usually sells for more than the bare watch. If you're buying to keep, a bare watch can be the better deal. If you might resell, pay for the full set.

Mechanical watches need a service every several years, and a brand service on a luxury watch can cost hundreds. A recent service with paperwork is worth paying a little more for.

Sellers can ask anything. Open eBay's sold listings to see what buyers actually paid in the last few months.