In your case it would have been easy "I have an exploit that let's me get the e-mail address of every Google+ account". Then they could decide how much that's w

In your case it would have been easy "I have an exploit that let's me get the e-mail address of every Google+ account". Then they could decide how much that's worth to them. But I also don't see how that would play out. If their offer is too low what would you do then? You can't sell it to someone else as this is most likely illegal and just keeping it for yourself is also not a great choice.