It's actually true. There are bounties out there that that didn't became successful at the start, But after a few months or years, You were shocked that it still lived to it's expectations. So, if there are bounties out there that you know has potential, Don't sell it. It may cost you thousands of dollars in the future.
I'm hopeful due, I have a lot of bounty rewards that I can't sell right now, it could either be the project has already failed or they just pause now, I don't know anymore, I haven't followed the projects I participated in bounty campaign before but I know one day I'll be interested on checking them especially when the altcoins season begins.