Pretty dumb policy if you ask me. If a developer is throwing up junk and they sell it they should pull the money from the sellers account and refund you. If you are a scammer they could easily create an algo to prevent future refunds, not hard really.
Sounds ridiculous but throw up a ripoffreport or something, sucks for Themeforest but that policy is pointless. Sellers don't drive the business, customers do.