Instead of monetary offers, some sellers will accept Swap Offers - offers of an item of appropriate value in exchange for the item being sold. The swap offer process works in a very similar way to the standard Make Offer process.
1. If the seller of the item you are interested in accepts Swap Offers, you will see an entry stating:
Swap Offers are accepted for this item. [Make an Offer]
2. Click on the Make An Offer link and enter a description of the swap you are proposing.
3. Click Proceed and you will see a confirmation message confirming that your swap offer has been passed to the seller.