INFORMATION FOR COLLECTORS

Detecting reperforation jobs on scans — are you tired of buying reperforated stamps on eBay? Here's how to detect most of them before you bid.

Evaluating feedback on eBay — 97.6% positive feedback: is this a good rating or a bad one?

What you need to know about sniping auctions on eBay — a guide to online sniping services and standalone programs.

U.S. classics: comparing the 24¢ 1861 and 1875 proofs — how to detect inexpensive proofs altered to look like expensive stamps.

U.S. classics: natural straight edges vs. clipped perforations — one is normal on many 19th century U.S. stamps, the other is a profoundly serious defect. Here's how to tell one from the other.