Depends on what part of town you are in.

Lower income areas have tons of parts houses and they always seem to be very busy. Sometimes even guys working in the parking lots trying to keep their stuff running or passing safety/emissions.
Middle income there are still quite a few of the usual parts houses, but they are less busy and seem to mostly sell car wash stuff and windshield wiper blades. They seem to be busy on the phone though supplying local repair shops.
Upper income parts of town there are none to be found.