I attempted the parking lot shop, but felt very conspicuous when I was doing it. Even at 7 pm, it was dark (I did it in the winter), it was difficult to read many of the names on the vehicles, and even harder to see the state name on the license plate. Commercial license plates can look very different than passenger plates. And you're not supposed to get out of your car to get a better look. I was surprised by how many guys hang out near their trucks and eyeball every car that goes by. It was too uncomfortable for me. I went to 4 hotels in a suburban area near a fairgrounds/event venue and there were about 4 trucks per location. I got the required info for maybe 1 truck and didn't even bother to submit a report. Maybe if I had better eyesight, it would have been worth it.
Not every shop is for every shopper. Good luck if you try it!