That's quite an accusation to make... You can watch your lambs weighed at auction. You can honestly tell me that some abattoirs won't fix their scale or alter the trim spec to suit them??
I regular draft my lambs in the morning before market and even have my scales set back 2kg and still seem too always be 2kg per lamb less than they were 2 hours ago at home when I get to market... but atleast iv seen the weights at market rather than just hoping the abattoir is honest ... could send the best of the best lambs there and they could still tell me they had too trim half of it off