While some people are certainly "fly by night" and try to skirt any rules they can, most are not like that. For example, I know one guy who routinely hauls placardable HAZMAT in a van, with no CDL and no placards. I keep telling him it's just a matter of time before someone hits HIM, and then he's screwed. He doesn't care. But examples like that are exceptions rather than the rule. Running unlettered, for the most part, doesn't mean "fly by night" or shady or up to no good. It is, nonetheless, less-than professional, for the simple fact that it lends itself to jumping to those conclusions.
As for the tickets, reasons like that are one of the many reasons people use to not letter their vans. Most of those reasons, the "less tickets" in particular, are self-delusional at best. There are no statistics whatsoever to back up such reasoning as commercial vehicles will be cherry picked out of a pack to be cited for speeding or anything else (it's true of regulated Commercial Motor Vehicles, but it's not true of unregulated commercial vehicles). It sounds good, and makes sense, but it's same reasoning people use to think their out-of-state plated Toyota Camry is what got them a ticket out of all those cars on the road who were also speeding. It's faulty reasoning, regardless of how deeply they believe it. Like I've said, people have all kinds of reasons, and they will staunchly defend them, regardless.
I think so. Not necessarily having the box lettered, but at least signage on the doors. It states purpose and intent, and puts the industry as a whole in a more professional light.