You should take a minute to read up the definition of harassment. You do not have an exclusive right to a bare minimum charge of any good on the market board. The prices are set purely by supply and demand. You are feeling grief because you found a niche market to make a quick buck and now someone has decided to bust your game plan. You have two choices at this junction, A) buy up his supply and re enter the goods at your (rediculously inflated) price or B) move on to another commodity.
And sprinkle in a few basic business lessons along the way. Could save you some hurt and embarrassment down the road.