More definite acceptance of terms before locking offer from widget

I have several important conditions that I need customers to agree to prior to sending their trade-in. This is especially important because of my cost exposure ($15+) to ship an item. I would like to have a more definite way to ensure customers have read and agree to my conditions. e.g. they have to type their initials in a box beside each term… or something similar to that. My end goal is to have no doubt that the customer has agreed to my conditions prior to me incurring the shipping cost.