"Jeg selger": the g is not pronounced at all in Standard Østnorsk (spoken in and around Oslo). Google gets it right (barring the fact that the robot sounds drunk): https://translate.google.no/#no/en/jeg%20selger
But: "En selger" (a salesman) or "En telefonselger" is pronounced with the g (hard g sound). https://translate.google.no/#no/en/en%20selger
They mean the same thing.
If you use the possessive before the noun, the noun is in its indefinite form (e.g hennes datter). But when placing the possessive after the noun, the noun is in its definite form (e.g datteren hennes).
Other examples: mitt hus (my house) and huset mitt (my house); din hest and hesten din (your horse)
You could say "hennes datter" (her daughter).
When the subject (daughter) comes first, which seems to be the more common way in Norwegian, it needs to be definite (datteren).
I think of it like this:
"datteren hennes" roughly translates to "that daughter of hers", which can be said in English, but is uncommon. You wouldn't start a sentence off with "daughter of her(s)", you need the "that" to make "daughter" definite.
I can't judge whether the sentence you entered should have been accepted if you don't give the full sentence. We have several accepted answers containing "telesales" on our end.
In the future, please use the report function and mark your sentence as "should be accepted".