Multi-vendor users - how are you managing fees?

I am working with a company so that I can sell their products through my site. We are still working on the details and both of us are concerned about fees. One option is for me to take the sale and then transfer the money to them. The problem is that I would incur fees and they would incur fees for a single sale. Another option is to find a way for the product, when purchased through my site, to go to their paypal shopping cart. Has anyone done this before? The last option is for me to setup their products as a vendor. If I were to do that, how are fees handled?

I'm sorry if these are newbie questions but I am still very new to CS Cart.