List the inventory you can spare and describe what would be worth the same to you. Both sides are priced at the published rate card, so the comparison starts from a real number.
2
Agree the balance
Swaps rarely land exactly even. The gap is closed by adding a face, a week or a daypart until both owners sign off on the two values.
3
Both runs are proved
Each side delivers proof photography or a play-out report for the other. The swap only closes once both campaigns have run and both sets of evidence are in.