The MO gets an aircraft in for an annual, not seen it before, goes through the paperwork and inspects the aircraft. ADs are found either not done or not done correctly, the customer is informed and realises he will have to have the work done and pay this additional cost. Aircraft finished back in the air, bill sent. Customer now complains about the cost, eventually the MO compromises reducing the bill just to get paid. The following year the customer takes his aircraft back to the previous MO, because they were so much cheaper.
Not always the MOs fault.