we used to do a lot of hire cars and driving schools
we found that the vast majority were quite worn at highish mileages and we insisted on replacing dmf's
the same company also used a national chain who did not fit dmf's a lot of the time
we had zero returns for justified clutch faults
the national chain had a very high return rate
i do believe that bye changing the dmf you would be saving your customer money in the long term

best regards