I am affiliate with website that pay $12 for Free Trial Signing-up. For first 2 month, I can not make more profit from advertising this site on Adword. But after I adjust my campaign, the third month I can make $2,000 from this site (about 160 free trial signing-up). Then 4th month, that website changed my condition of commission from $12 for free trial signing-up to $12 for paid signing-up, they told me that because there are a few people from free trial member enroll to paid member. I don't know any other websites which offer commission for free trial signing-up will be same as this site or not (if you can make more money from them, then they change condition of commission).
The first thing to know is to know if they are changing the term conditions exclusively for you (this already happened with me) or they are changing for all customers. Provide the advertiser name and we can check the actual conditions. Anyway you should promote at least 10 different advertisers: if someone drops CJ network, stop converting, kicks you out or do something like that, this would affect only 10% of your income, not 100%.