Take it up w/ the market manager. Maybe put some rules in place that resellers can only have 20% of their total wares from off farm sources.
Our market does it by weight. So for example, if I have 500 lbs of produce and poultry to sell this week, I can have up to 100lbs of "resell" items. It allows for those who want to resell (or had crop failure), but still maintains integrity of the producer only market.