Capturing Percentage of Payment and Giving the Rest to Business Client

Hello kind SitePointers, thank you for always being so helpful. I would appreciate any insight on how to approach this business model I am considering:

I would like to give businesses an opportunity to advertise and sell their services on my website. In turn, any payments that are made on my site by a visitor would incur a small commission (paid to me) and the rest would go to the business.

What is the best way to execute this process?

Originally, I thought to accept the payment myself and then send the money (minus the commission) to my business client. The problem with that, as I see it, is that I would incur a fee from the payment processor initially, and then when I send the money to my client, they too will incur a fee from their payment processor. I fear that the fee on their end PLUS the commission they would owe me might make it uneconomical for them to do business with me. Essentially, I would like to avoid the fee being charged to my clients and simply incur one fee on my end.

I am not asking for specific coding advice, just general ideas for carrying this out. Suggestions as to what payment processor I could use (I was looking at AlertPay) are also appreciated.

Thanks for your patience and assistance!