What would you want?

For most affiliates involved in gambling niches, I think the widespread answer to that question will be that it's going to depend on the number of months for which the average customers remains subscribed. The affiliates you want are the ones who already appreciate that that's far more important than the commission percentage, per se.

There are a lot of hyped-up gambling-oriented products/sevices/memberships whose average subscription duration is around two months or even a little less, and I understand that they're the ones that have great difficulty attracting serious, pro-affiliates who actually promote successfully and achieve good sales.

I suspect that this kind of niche is perhaps a classic illustration of how much better it is, from the vendor's perspective, to have a handful of affiliates who can regularly produce a few dozen real buyers/subscribers, than a hundred or so affiliates who rarely make a sale between the lot of them. Attracting the minority of affiliates you really need is all about proven conversions, really - and in the case of recurring-commission products/services, that means proven customer-retention, too.

With gambling-related things, that's typically fairly unimportant to the customers, who typically care only/mostly about proven, independently verifiable results.

"Free trial offers" of the kind referred to by the OP can have extremely high conversion-rates for targeted traffic, and after that point, subscription renewals (or "lack of cancellations", if you prefer to look at it that way) depend more or less on "results actually achieved".

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