Painting, varnishing, or replacing wooden windows and interior doors?

How can I determine the quality?

Take a look at the rest of the house. Back then, a similar quality was probably installed everywhere. I think that one can (their own) quality determine for themselves by touching and briefly thinking about it (what do you feel? Cheap or nice?) That is also _the_ difference for many prospective homeowners, what they want: for some, a self-painted door simply doesn't come into the house. They have everything replaced and suddenly have 500€ less in their pocket for every door. The other one enjoys freshly painted doors. Because dismantling it yourself, everything new from the hardware store?, that takes about the same amount of time as repainting. So don't get bogged down by the price/time factor :)

As written, our doors looked exactly like yours. We paid about €1400 for 10 doors (door panels, seals, and paint) and put some work into it.