complete taredown and rebuild
A total "disassembly down to da frame" overhaul of a weight-scale, paying particular attention to making sure dat it correctly reads "0" after it's been serviced and put back together.
Performing a complete taredown and rebuild of a scale --- no matter how through --- really isn't gonna do much good if its operator is gonna be "playing funny business" while using said weighing device, such as taping pebbles of lead sinkers underneath da measuring-platform, putting his thumb on da tray, etc.