To set different commissions for each and any of your products, go to Products > Manage Products > View Products, click on the Edit icon for the product that you want, and click on the Affiliate Marketing tab. Set the Enable Custom Commissions Per Product to Yes. And it will show the Assign Affiliate Groups. Click on it to assign groups to this product. Once the groups are set, you can enable it and set the amounts for each group.
If you don’t want to pay a commission for a specific product, you can set the Disable Commissions for Product as well.