Did not recieve item during trade

Note: I am an experienced trader; have been playing PoE since the early days of PoE 1.

I used the trade web site to find and arrange a trade for an item (Oaksworn Sigil Crest Shield for 1 Exalt).

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I went to his hideout, opened trade, put in the Exalt, they put in the shield, I hit accept and then left party.

Went back to town and the shield was not in my inventory but the Exalt was gone.

I message the seller, and asked them to verify if they still had the item and they said "I dont"

Not sure if this is a bug or a scam, but I've done many, many trades and this is the first that every had an issue with.

Just to check, since a similar thing happened to me the other day, have you checked your other weapon set?
Even if I do not have auto equip turned on in settings, and even if I did not have the empty weapon set in use, a crossbow I bought ended up there and it took me a while to realize that was where it went.

I assume this is not intended behavior so if it is any use these are the circumstances I remember.

I had nothing in weapon set 1, and I had a crossbow in weapon set 2 which was active.
I auto-equip is not checked in options Game tab.
I did a trade with a player and then went to my hideout. Once there it seemed the item was gone, but I later realized it was in the inactive weapon slot.

Never mind. It seems that shield was automatically equipped on my weapon swap. I was using "gear set 2" with a one hander and shield, and had nothing in "gear set 1." I discovered today the shield was in my off hand for "gear set 1."