If you want to get cheating out of USTA league tennis get rid of nationals/regionals or crowning any type of champion. My nonUSTA leagues rarely if ever have any sandbagging or people self rating too low because there is no other reason to play and try to improve. At then end of the season the winning teams are kept intact and move up to the next level. People often try to play up a level to get better competition and are not scared of losing matches.
It is amazing how many USTA team captains will game the system to their advantage and deliberately have self raters that are far too low, or sanbaggers and then throw their hands up and say I didn't break any rules. They actually believe as long as the get away with things then their honor is intact.