Although you didn't say in your post, I'm assuming you recommend telling them that the computer is damaged when you sell it? Uh... that's why I never buy expensive stuff on eBay. Too much risk in getting scammed or ripped off buying damaged goods.
By the way, I'd have my friend replace the computer. They get to keep the old one. If I did something like that, I'd insist on replacing. What kind of friend would leave you with a 1200 repair bill even if was an accident?
What kind of friend let a friend pair for an accident? What happend, happend, if he offers to help him get fixed then good, else well.... is a material thing