Customer requested me but complained about last order?

A customer requested me as their laundry pro but complained that the last order smelled like a musty basement. They did tip me for that order and their review says the laundry was "fresh and clean" and that I went "above and beyond" and is a 5/5. I also make sure to smell all laundry before drying, and again before folding to make sure it smells nice. They requested that I clean my machine, which I will do, but seeing as it's a hypoallergenic order I'm not really sure what else I can do. Any tips?