TL;DR: If you find an exploitable bug in a high-profile web site and discover that you're ineligible for a bug bounty, sell it to the bad guys instead. They won't treat you like s##t. ;-)
Say, you sell it to someone and to the best of your knowledge they want to claim the reward for themselves. To justify the increased price you received by selling it to a third party instead of submitting it for the bug reward you could say that the third party intends to claim the bug as his own work and the professional cred they'll receive justifies the increased price.
[1] http://www.techrepublic.com/blog/security/guess-whos-buying-...
"Hey, that building has a broken window."
IANAL.