Adding newer information to this old thread...
Recently I found that routing to a marked gas station that was on the intersection of two major (with median) streets routed me past the station to the next local street and had me come up "behind" the station were a road didn't exist. I fixed the issue by adding a service road to the entry/exits.
Example:https://www.waze.com/editor/?lon=-122.0 ... =7&env=usa
I was traveling EB on Thornton so turning left onto NB Fremont and an immediate right into the driveway is the correct path. Waze sent me past to turn left on Moraine Street (NB) and left on Turner Pl (WB).
So it seems that adding the entry/exit driveways can make a big difference for gas stations routing and this seems key for Waze since there is (now) advertising tied to it. I had clicked the popup flag even though I go to that station regularly and was frustrated it routed me incorrectly.