Work more on "Oh shit! You need to buy this NOW!" more than "Here's why you should take my word on this."..
They probably either had bad reviews in the past and/or bad or non-updated members area. Either that or people are writing "reviews" and are causing chargebacks because of inaccurate info.
If you have a review site that you really want to push a sponsor that won't let you, just have an "Other related sites you might like" on the page. If you really want more sales from them, make the promo and call to action look better than the reviewed site. ;)
Or just related niche sidebar ads, those get clicked on pretty decently for the most part.
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