I don’t think the dogs’ ability to smell things is in question, but the ability of humans to reliably use that sense of smell and not inadvertently get the dogs to respond to an accidental or deliberate signal from their handler.
Ultimately, the dogs want to please their human, not sniff out drugs, and if police are looking for some pretext to search a car, then signaling with or without drugs will please the human.
Dogs should only be used once a warrant is issued to help speed up a search. At which point, if they aren’t good at it, they’ll eventually just stop using them. If they can be used to bypass warrants entirely, then that is their usefulness, not how good they are at finding drugs or not signaling when there isn’t anything to be found.
That’s what I meant about it being more dependent on the owner rather than the number of seats. You can’t tell at the point of sale how many people each buyer is going to be transporting regularly, but it plays a huge role in how efficient that vehicle will ultimately be.
A four seater truck is horrible if it’s just the owner riding alone in it, but pretty good if it’s full and being driven instead of 4 single occupier trucks.
Though a 4 seater sedan is even better, so I was referring mostly to higher occupancy vehicles, like vans that can seat 7+. One of those could replace two sedans if filled to capacity. Or a 50 seater bus, or a 300 seater train (or whatever capacity mass transit options have).