I agree there is the potential for some to commit fraud on these tags. But, I do wonder about casting that charge in all cases. What about the many vehicles out there that prior to the mid 1950’s had the vehicles registered using the engine number and subsequently that engine was changed out to something else? I have seen many cars and trucks at many car shows with obviously replaced engines that more than likely legitimately have titles /registration and have a repop tag secured to a pillar or floor pan or cowl.
IMO seeing a repop and/or wrongly located tag on a vehicle being advertised for sale raises the bar for the potential buyer to exercise additional diligence, but not necessarily brand the seller as a fraudster.