If we are to gain a clear picture of the people to whom Jesus brought the good news, our starting point must be the fact that, when we look at the various designations of the followers of Jesus as they are given in the gospels, we come to know these people from a double perspective.
They are repeatedly called ‘publicans and sinners’(Mark 2.16 par.; Matt. 11.19 par.; Luke 15.1), ‘publicans and prostitutes’(Matt. 21.32), or simply ‘sinners’ (Mar, 2.17; Luke 7.37, 39; 15.2; 19.7).
The deep contempt expressed in such designations shows that these phrases were coined by Jesus’ opponents; Matt. 11.19 pr. Luke 7.34 confirms that explicitly.
In the world of Jesus, the term ‘sinner’ had a quite definite ring. It was not only a fairly general designation for those who notoriously failed to observe the commandments of God and at whom, therefore, everyone pointed a finger, but also a specific term for those engaged in despised trades.
We have lists in which proscribed trades are collected. These are in part trades which were generally thought to lead to immorality, but above all those which by experience led to dishonesty: the second category included gamblers with dice, usurers, tax collectors, publicans and herdsmen (these last were suspected of leading their herds on to other people’s land and pilfering the produce of the herd).
When the gospels talk of ‘sinners’, they are thinking of those occupied in despised trades as well as those whose way of life was disreputable. This is clear from their terminology, especially the composite phrase ‘robbers, deceivers, adulterers, publicans’ (Luke 18.11), which is paralleled by analogous collections in Rabbinic literature, e.g. ‘tax collectors, robbers, money changers and publicans’ (Derek eres 2); ‘murderers, robbers and publicans’ (Ned. 3.4); cf. ‘tax collectors and thieves’ (John 7.6). The publicans are the typical "sinners" in the gospels. They, in particular, were outlawed.
(Jeremias, Joachim. 1971. New Testament Theology. New York: Charles Scribner’s Sons., pgs 109-111)