Various words for professions end in -logist or -nomist. I hope I do not do terrible injustice by treating -nomer as a synonym for -nomist. These seem to come from the Greek words logos and nomos and the suffix -istes. Sometimes they can both appear with the same initial segment (astrologist/astronomist or agrologist/agronomist or ecologist/economist), but the meaning is often different. However, the differences in meaning appear inconsistent to me.
Did the ancient Greeks have both -logists and -nomists? If yes, what was the difference? I know that the underlying two nouns are different, but I am specifically looking for differences between the corresponding derivations.