Call his bluff

tell him you will arrange for a courier to collect your set of fans plus his "fucked" ones and will refund him the £40 for yours plus a tenner for the knackered ones as well

If he is genuine you get another set of fans for £10 which probably just need a simple repair (usually just corroded terminals).

and if he is lying you have him by the balls as he will end up with no fans at all if he has to part with both sets.