No one is going to expect a price to plummet that much. The only time someone screws over the "market" is when they have a lot of something and constantly undercut, which even then the price isn't what's killing the market, it's the supply.

Banana males can be had around 200-250 right now, I got a banana spinner for that and it was a good deal. According to your theory they'll all drop down in price, but right now the cheapest 3 gene male that includes banana on morphmarket is 350 (300 if you count super pastel as 2 genes).

The market isn't going to be affected by a single person with a single animal cutting the price in half.