One thought I actually had was that somebody owned the bounty hunter droids, and hired them out for a huge fee to someone who wanted the get the bounty. The droid owner would get paid no matter what for renting out the droid, and the customer would carry the risk if not getting paid if the bounty escaped or a different bounty hunter got it.
This is all non-canon, for what it’s worth.
This is all non-canon, for what it’s worth.