A week after Roy Morgan Research reported that retail bank customer satisfaction levels had fallen to their lowest level since 2013, DBM Consultants report that business customer satisfaction has fallen to a four-year low.According to DBM's latest Business Financial Services Monitor, all the big banks have lost ground this year (DBM only reports on the big banks).DBM said the overall drop in satisfaction was driven by microbusinesses, while the responses from small and medium business respondents were more positive.Large businesses gave the banks the highest ratings and also the most improved ratings. The banks get an average rating of 7.8 from large companies - the highest rating they have ever received from this segment.However, microbusinesses drive the overall DBM result, given their large number. Overall, Commonwealth Bank has a rating of 7.2 (out of ten) - down from 7.3 in December. Westpac has a rating of 7.2 (down from 7.3 in December), NAB has a rating of 7.1 (7.3 in December) and ANZ has a rating of seven (down from 7.1).