Montana plates are a huge red flag, pretty much unless the seller lives in MT, they just scream "shady licensing" to me.
Dan
It's also possible that we plebes aren't thinking like a wealthy person. The current owner probably actually owns property in Montana and the licensing isn't to an LLC that shares a PO box with 25 other LLCs and a law firm.
The car may actually be in a garage in Montana, too, and used a few weeks a year each summer, if at all. So the seller (Silver Arrow Cars Ltd of Beverly Hills) was chosen to represent the owner because he/she has a residence there, too.
Just speculating, though.
For example, if memory serves Tom Hanks' FJ40 had Idaho plates but was being listed by Bonham's in L.A. But Hanks owns a huge ranch in Idaho and the Cruiser was there. Nothing shady about it.