Final answer:
Ignoring the complaints on social media.
Step-by-step explanation:
In this case, the action that is most likely to discourage customers from returning is ignoring the complaints on social media.
Many customers took to social media to complain about the lack of salespeople during the department store sale.
By ignoring these complaints, the store is not addressing the issue and showing a lack of concern for customer satisfaction.
Ignoring customer complaints can lead to a negative reputation and a loss of customer loyalty.