Exegesis:

ēlthon de kai telōnai baptisthēnai ‘tax-collectors also came to be baptized.’ The aorist tense of ēlthon does not imply that the tax-collectors came to John only once but indicates progress in the narrative. For baptisthēnai cf. on v. 7.

telōnēs ‘tax-collector,’ usually an underling, employed by Roman tax officers or Jewish tax farmers to do the actual collecting, despised because of this direct or indirect connexion with the Roman government and his reputation of enriching himself at the expense of the people.

didaskale ‘teacher,’ Greek equivalent of Hebrew rab or rabbi, a polite form of address rather than designation of somebody whose occupation is teaching. This applies also here since John is not a teacher of the law but a prophet.

Translation:

Tax collectors. Terms for taxes and/or custom duties often are borrowings from the national or trade language. Where no specific term is available one may use a descriptive phrase, e.g. ‘people who collect shells (i.e. money)’ (Ekari), ‘those who extract (or, profit by taking) money for the government.’

Teacher, cf. on 2.46, is used as a form of address to John (here), and to Jesus (in 7.40; 9.38; 10.25; 11.45; 12.13; 18.18; 19.39; 20.21,28, 39; 21.7). If the usual rendering of ‘teacher’ cannot be employed in this position or context, one may have to use ‘sir’ (Kituba, Pohnpeian), or another term used in polite address: Chinese (L) has an expression literally meaning ‘(you have been) born before (me),’ which is the usual thing pupils say to their teachers in school, besides being the usual polite form of address: in Tboli ‘friend’ is a respectful form of address that can often (e.g. in 7.40) do duty for ‘teacher,’ which is never used in direct address.

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.