It may not be the managers fault but a poor service is their responsibility. Managers need to take responsibility and be accountable for the way their employees do the work.
Are employees adequately supervised, inducted , given feedback and trained. If they have no previous experience they will need more support. On boarding is particularly important when employees were hired who do not already have a customer care focus.
If a, take it or leave attitude emerges, then managers must challenge this but often it’s the manager who is modelling the behaviour.
Employees are expected to be polite and friendly , helpful and respectful, irrespective of the customers behaviour. But do they know how to deal with an unhappy, disgruntled or rude customer? The manager should have established this as part of the recruitment interview, followed up in the induction program. Employers can not take for granted that potential employees know how to treat customers especially when they are dealing with some one who is blaming them for something either out of their control or not part of their job. They may not appreciate they are the face of the organisation or feeling the criticism unfair or wrongly directed take a defensive even aggressive position. The what do you expect me to do about it shrug of the shoulder can escalate a minor criticism into major complaint about the attitude and rudeness of staff. If this all sounds obvious and rudimentary to you and me it can not be assumed to be obvious to people who are by the managers own definition not the type they would previously have recruited.
It’s common sense that staffing levels affect customer care. Over worked and harassed staff are more likely to respond inappropriately but too many staff can also be a problem. The customer who sees lots of staff standing around apparently doing nothing yet is unable to get seen to gets frustrated and then annoyed. In a five star hotel I recently experienced the sight of the specialist cushion plumper. Someone whose sole responsibility was to go round the sitting areas plumping the many cushions! Whilst guests struggled to attract the attention of anyone who would take a drinks or food order. Being clear who is responsible for what is essential for the smooth running of an operation but excessive demarcation is the enemy of good customer care.
As a manager always remember the customer isn’t interested in your problems.