I agree that having some more guidance to get us on a consistent path would be nice, but waze needs to decide how gas stations will be handled here first.
There are many parking lots (at least on the MD side of DC) that were added by the IGN team. It seems that suppressing map problems and traffic reports from cars in parking lots was being addressed by the IGN team by putting in parking landmarks. These landmarks in my experience typcially included the buildings as well. An example is the Annapolis Mall.
The other issue is that quite a few landmarks seem to have come in with the base map. Some of these (particularly golf courses) over the course of fiddling with the landmark classifications have been given a default class. With the introduction of the gas price feature, gas stations have been made the default landmark and these landmarks now show as gas stations. This is likely the created by admin(6) gas stations that you are seeing. Example here
I guess all I'm saying is that many of the problems here are largely traceable directly back to waze and not to the editors.
My understanding is that when routing to a gas station from the gas station category list in the US the current landmark layer is not used. In other words the imported gas station data is currently separate from the landmark layer. It also my understanding that the gas station data will be made available in WME for ongoing maintenance by the editors, but that this has not happened yet. Until we see how this is done, it seems to me that it is premature to develop best practices guidelines.