I think "partnership" is not the appropriate idea instead, hiring the service of a reputable manager to advertise the gambling site. That alone is the only job of the campaign manager and not to the point it will follow the partnership terms of the gambling site as these owners might take advantage of the popularity of the gambling site.
In conclusion, since those new gambling sites hire some managers and are willing to spend money on marketing, we can assume they are really serious about promoting their site. We should be just aware and vigilant before using these sites as campaign managers don't have a way to detect if these new sites will be turned dishonest someday.
That's beyond the manager's control.