I don't think it is legal for a livestock market to do that. You should check with Packers and Stockers Administration. At the very least look at the tariff (charges allowed) sheet at the auction. They should by law have it easily visible and if they charge shrink it by law is on that sheet. Sellers are getting the shaft on that. Most of the actual shrink occurs from loading at farm to arrival at market, in worst case it's costing you 4% shrink (3% before they get to market)