I have products and a service that I offer on my site. I am negotiating with the owners of a site that deals specifically with my client base and has about 100,000 members. What would be a fair percentage to offer them for sales based on click thrus from their site. We would be advertising them as well, the difference being that my income is totally based on product sales, where thiers is almost all advertising.
Depends on the marginal costs and revenues. If you can process more orders without increasing costs you can offer a huge profit share (even 50%), still make money and hope you would do direct business with your new customers in future. It might also stop your partners from doing what you're doing as they get enough to accept the money and avoid hassle providing the full service themselves.