It's not a 1/1 but if you are a supercollector of that guy you'll probadly pay a little more. Not alot more. Depending on the serial number series there may be 4 or more serial numbers of the guys jersey number
13/25
13/99
13/199
13/299,ect.
If that guy told you it's one of a kind and it's a one of one then he's an ebay seller not a collector. Any collector would tell you it's not a one of one unless it says 1/1. There are loads of crappy sellers that sell cards they say are one of one because either it's his jersey number, first or last in series, or any freaky weird mathematical representation they can think of to say it's one of one so some sap can pay more for the card. Sell it as his jersey number but don't say it's a 1/1 it just makes you look stupid.
13/25
13/99
13/199
13/299,ect.
If that guy told you it's one of a kind and it's a one of one then he's an ebay seller not a collector. Any collector would tell you it's not a one of one unless it says 1/1. There are loads of crappy sellers that sell cards they say are one of one because either it's his jersey number, first or last in series, or any freaky weird mathematical representation they can think of to say it's one of one so some sap can pay more for the card. Sell it as his jersey number but don't say it's a 1/1 it just makes you look stupid.