Not listening to the customer as well as disagreeing with the customer is a biggest mistake one can make. Even though the customer is at fault ignoring their talks is the biggest drawback even for an existing client.
well, I believe that there are, in fact, mistakes ont only one mistake. For instance,
one should avoid:
lying to customers,
not respecting deadlines,
not answering their queries and request,
and not accept their complaint and show understanding
