Ditto to go with by the pound. I have been to sales where this was done and it is easier for both buyer and seller. You could even have a separate scale for them to try and weigh their own before getting to the sales table. Hey, even Eleanor Burns store did it at Paducah to sell all their scraps.
Also this method results in full bags and less room taken up at the cash our area since 1. No haggling over measurements, no time needed for sorting and pricing, and bonus all scraps can be easily sold.