Friendly means acting in a non-threatening manner toward and/or showing kindness

Kindness

Kindness is the act or the state of being kind, being marked by good and charitable behaviour, pleasant disposition, and concern for others. It is known as a virtue, and recognized as a value in many cultures and religions ....

 to someone, as a friend would behave. Thus friendly implies a mode of friendship as distinct from amiable or genial. Professional service is expected to be amiable or genial but not necessarily friendly. The opposite is unfriendly or even hostile.