Barter is the same as money. Cash, chickens, items in trade, all are treated the same. It's all got a value.

Your client "bought" the traded in item for some value that he set for it. That is his Cost for selling it later. He still "sold" the original item he had on sale, under non-cash conditions.

The IRS has guidance for this. You can google:

irs barter

https://www.irs.gov/taxtopics/tc420

https://www.irs.gov/pub/irs-utl/OC-Barteringandtrading-eachtransactionistaxabletobothpartiesFINAL.pd...