I'm wanting to do mods on clothing. However, I'm not sure how to handle the monetary process. If they bought a product not through us, how would that be linked to us? Do I ask for a receipt as part of the modification purchase? If we are a new business I don't know if we could do a partnership with those other businesses.

Perhaps they could purchase those modifications, and as part of that, include a link or description of the item?

I've never seen a business model like this so I have no reference. I'd like to do it this way as it would involve only two sets of shipping (to us, to customer) as opposed to three (customer, us, customer).

Thoughts or suggestions?