There may be sayings about engaging in business with friends or family.
The friend would be providing a service, and besides paying you some of the proceeds, you might wish to have some kind of "accounting system" set up.
If the number of items (5) is small, then the accounting of where all the money goes might be simpler, on an item by item basis.
If the arrangement grows into dozens of items, some that sell fast, and some that sell slow, perhaps you and your friendly service provider could agree on a simplified spreadsheet, and a reporting frequency (by item; weekly; monthly; etc.), and accounting for your items separate from your friend's stuff: