when someone use your username name and link then you should give information to the bounty manager which he could see all activities and bounty manger should take the big action against that person.
for now only that is what we can do, but is that what we can do forever? Bounty cheaters are very annoying because they can easily get tokens that they shouldn't get. there must be some security on the Bounty that can prevent fraud for the convenience of the bounty hunter. but it's not easy to make it, all need a process, so we can only take care of ourselves if we follow the Bounty.