The correct answer for your job is that you should do what the customer wants.
However, from a mathematical/statistical perspective there is a clear answer: you should return the median of this data, not the mean (i.e. you should return '3', not '3.4').
If you are reporting the mean, you are presupposing that it makes sense to add the data together.
To see that it makes no sense to add the data in your case, consider that the numbers 1-5 are just labels for how the customer feels: they don't represent quantities. You could equally have used the five categories 'Very bad', 'bad', 'neutral', 'good', 'very good' instead of the numbers 1-5, in which case it would be obvious that adding together these categories makes no sense. It does make sense to order the categories, however, so you can always return the median (in this case the median is 'neutral').
To return the mean instead of the median is deceitful: it creates a sense of quantifiability which is not warranted from the data.