I'm sorry to say this, but you are not allowed to resell humble bundle keys.
I think they may have changed their stance on this, as they do have options to create other pages for the keys you don't want/need. I have sent them an email to confirm this, so until I hear back I won't execute any trades.Nope, humblebundle only allows you to use your keys for personal purposes. The other users you see are not following the rules.
If they have changed, let me know!
I doubt they would though, it's supposed to be "charity"