O'Reilly Auto Parts in Waterloo is praised for its helpful and professional staff. Customers highlight the employees' patience, politeness, and willingness to go above and beyond, such as helping in the rain or thoroughly cleaning battery cables. The store provides reliable service, including battery replacement and parts orders, with staff taking their time to do a good job. While most employees are friendly and accommodating, some customers note that a few staff members have limited knowledge about certain products. Overall, the store has gained loyal customers thanks to its good service and friendly atmosphere.