Return the FG and move on as stated above. It’s. It uncommon for people to send FG to “reserve” an item. Although it’s not supported by d2jsp staff, it’s not uncommon.
You’ve dragged it out longer than it needs to be. If you don’t want to trade with said user, return his FG and if you’ve already blocked him for whatever reason, move on.
If you have any other questions, feel free to PM me directly.