The article focuses on distinguishing the characteristics of the quality of services that support better financial results achieved by bank branches and the increase in labour productivity. To achieve this a method of decision trees was applied to data proceeding from branches of a big retail bank. The analysis indicates that big branches located in towns generate better financial results despite the fact that the location, working hours and a friendly attitude of employees are far from satisfactory. High qualifications of the staff, including the share of employees with higher education degrees, constitute the most important factor conducive to good financial results. The branches with a relatively small share of persons with higher education degree should be advised to take more time to service clients and do it more carefully. It is also worth focusing on limiting errors in credit activities and devoting enough time to repair the effects of IT failures. It is also recommended to serve retail customer faster (in particular as far as settlements and deposits are concerned) and to serve strategic customers relatively slower. Providing adequate information on the telephone is also important.