It seems the easiest approach would be for them to have their own E-junkie Seller account with an affiliate program, then you could join their program and obtain their Direct Link code for that item to copy and paste into your site -- i.e., if they are already your affiliate, now you would also become their affiliate.
If they already have an E-junkie account as an affiliate, they can simply start a paid subscription in Seller Admin > Start/Update Paid Subscription to enable Seller functions for their account. Likewise, you can use your existing E-junkie account to join their affiliate program; our basic $5/mo plan would probably be sufficient. Use the Seller Admin and Affiliate Admin links in our admin panel to choose which functions you wish to see at any moment.
Direct Links work like an actual purchase button buyers can use to purchase directly from the affiliate's site (i.e., yours in this case); however, buyers are still actually purchasing directly from the merchant and paying them in full, so they get all the order data including buyer names/emails in their E-junkie Transaction Log, while the affiliate (you) would earn a commission on each order placed through such Direct Link(s).
This help page explains our affiliate system and related settings:
...and we also have a help page for affiliates here, explaining how to use our system from their perspective:
