I bow to your knowledge and let you take the case on for him
p.s. the subsequent sale - it's his own fault entirely on how much he sell it for. Why didn't he set a reserve? Why didn't he use another avenue of sale to minimise fees? Do you think he would have given the 1st buyer the difference had he sold it for more?!
I don't think so.
He has done nothing to mitigate his loss, something of which he agreed he should have done. Basing your loss on an event taking place that the 1st buy has no control over is absurd. I would love to hear that argument in court. What if instead he sold it for less, he just accidentally smashed it to pieces by dropping it? Do you think he could sue the buyer for the entire amount because his own fault for breaking it and it is now worthless?
It is his own fault not to sell it for the amount he wanted. No one else's.
pps
What if the buyer decides to go through with it, but the OP broke it before shipping, so he had to refund the money. The buyer then went and bought it elsewhere but cost him £100 more....he now sues OP for the £100 because OP didn't fulfill the original contract.
Is THAT right?
How could the OP be responsible to another person's action after the fact in a separate transaction? What has one got to do with the other?