While you may have the best intentions in mind and are able to demonstrate your highest levels of quality, at times, some people may still not be completely satisfied. I say this not to suggest that you should give up on improving your services and products or that you should give up on trying to reach those individuals and address their concerns, but more as an awareness message so you know that they exist.
They exists in all industries, professions, companies, organizations and it is very rare not to encounter them at some point in your career. However, when you do meet, stay positive, do your best to address their concerns, but don’t under any circumstances allow them to demoralize or frustrate you or your team. At the end of the day, you have control over your performance and contributions, not someone’s feelings or perceptions.