Derusting and varnishing

Moin,
I would like to start soon the "known places" (door sills, tailgate etc.). However, admit to me that it is probably better (and more permanent) if this is done by "competent" place (especially painting).
Is there anyone here in the forum who does something like that? (Of course with fina-target balance, it's clear!)
or an address where something like this (payable and good!) is done.
Good would be a contact 150 km around Kassel.

Thank you for your information
See you soon, Jans