we were very successful in finding charming and well-outfitted apartments in ideal locations in Oslo and Bergen. We used airbnb for Oslo and vrbo for Bergen. Oslo location was amazing, quiet neighborhood on the west side of city with tram and bus within a block. The Bergen apartment was on a pedestrian way, a 5 minute walk from where the Flam to Bergen ferry berthed. Perfect.
There is a risk to booking through 3rd part sites, such as booking.com, but that site's value is that for many reservations, it has a liberal cancellation policy (sometimes OK to cancel 24 hrs pre-arrival). I don't cancel but it's nice to have that liberal policy in the event of a trip interruption or delay. VRBO and Airbnb tend to have tougher cancellation policies (often rediculously so).
When I determine my destination, I spend a couple of hours reading about neighborhoods, check out transportation maps, etc, so that when I see an apartment to rent, I know how convenient it is to public transport and the sites I'll visit.