adding a sales agreement

Hi: I searched around and I couldn't find any info on how to add an individual sales agreement to a product. The sales agreement has to be specific to the one product that it's listed with, and the customer must agree to it before being allowed to purchase. Any advice would be appreciated. Thanks!

A simple solution is have a link in the full description of the product that downloads a PDF which is the sales agreement. "Note: You must  downloaded, read and agree to the sales agreement before purchasing this product - Click Here"
Then have a product attribute that they have to select to confirm that they have downloaded, read and agree to the sales agreement.
Alternatively in the checkout there is Checkbox "I agree with the terms of service and I adhere to them unconditionally" and in the terms of service say they must downloaded, read and agree to the sales agreement associated with the product before purchasing

Sounds great! Thank you very much!