what I would do is reply with an even more threatening email.....then id tell him to f**k himself...then id leave him even worse feedback than he left you...then every day for a month id bombard his email address with threatening emails....THEN id sign his email address up to all the gay porn sites i could find.......THEN...id tell him i have his address (which you would cos u posted out) then id find my way to the address and id bust down his door, zip tie him and take his plasma/lcd/blu ray/xbox/ps3 as payment for my troubles!
oh and then id go and get my item back from inside his house