I have a feeling that this is done with the help of staff. Once a person is able to get away with multiple accounts, he will try to expand to as much as possible.
We can only report such cases and hope that some action is taken by staff.
Multiple accounts is allowed, and staff don't moderate scams. Therefore, any reports made because of this will be marked as bad, and no action taken. The only time alt accounts may face consequences is when one of their accounts has been caught breaking the rules, and action has been taken. For example, if one of their accounts has been caught spamming or spreading ref links, and is banned for it. Only then will the alternate accounts be banned too, and that's assuming that the staff have enough evidence that the accounts are linked.
This isn't a moderation issue. Rather something that the bounty managers have to deal with themselves. The issue is that the bounty managers don't care. Possibly implementing restrictions on who can be bounty managers or post bounties/annoucement threads is the solution to the problem. But, it's no way a moderation issue.