How to check a serial number before you buy

Read the stamp

• Ask for a clear photo of the serial. It's usually foil-stamped on the front or printed on the back. It should be sharp, even and the same style as other copies of that parallel.
• Check the print run. The second number must match the parallel's real print run. A "23/99" on a parallel that is numbered to 75 is a red flag. Each card's parallels and print runs are listed in Jersey Match Library.
• Check the season. The number has to match what the player wore that season: see players with two numbers.

Watch for

• Reprints and customs: often unnumbered, or numbered in a way the real product never was.
• Altered numbers: scratched or re-stamped foil. Compare with photos of other copies of the same parallel.
• Titles that say "jersey match" for the wrong number, or that combine a card number with a print run ("#23 /99" is card 23, not serial 23).

Graded cards

For expensive jersey matches, a graded card from a major company settles condition and authenticity, and the label usually shows the serial. If you plan to grade a raw card, ship it in a card saver.