For the record: if you accept a trade like this by accident contact the seller immediately and report it here if you need admin assistance. If you complain about it 14 days later it makes it look like you got second thoughts. Also in this particular case a +3 for another +3 and 75k is a fair deal, there is nothing obviously wrong and you were not tricked into accepting it.
I didn't read it until after I found out I had lost money, I thought that Italian Sword + 75k was more than enough for Throwing Spear.
I believe that is not fair, but it would also be unfair if I got the trade reversed due to my lack of marketplace knowledge.
To my knowledge, Kafein appears to be hesitant to trade it back normally as he kindly offered to put the trade up so that tax needn't be paid. However, due to me being Australian and him being (er?), it may be easier and more reliable for you to manually reverse the trade.
I apologise for being rude and unreasonable, please see fit to take action where you wish. You and the rest of your team have better knowledge on these things than I do.