Hi Paul -
Perversely, that 144-scale model of the Bear may have been one of the seller's few originals!! Sorry to be the bearer of bad tidings.
Anyway, both the wartime and postwar models, made by companies like Cruver, Design Center, Leominster, Setco, Bevelite, Theatre Specialties, et. al., were produced in molds that were subject to pressures of thousand of pounds per square inch. Modern replicas are cast at atmospheric pressure. From a practical standpoint, what this distinction means is that replicas have small pits, bubbles, or occlusions if you look at them closely. You will see small pits in the bottoms of control surfaces, around the ribbing of canopies, etc. Originals had no air bubbles, given the pressures they were subjected to. Hence, no pits, bubbles, etc.
The thing that gave away the recent auctions of the Sea Fury and HE-111 were the raised "R"'s inside diamonds. The replica business is pretty much owned by a company in Fort Worth, Texas, which you can find at
http://www.aircraftmodels.com. This business was founded about 20 years ago by a guy named Dick Miller. Dick had a large collection of real ID models, and he was getting frustrated by the fact that some of his prize items were beginning to melt. He started reproducing things for his own purposes, and then began to offer replicas to the public. Dick initially marked his models with a raised "R" in a diamond (easily visible on the undersides of the wings in the aforementioned auctions). Dick found that unscrupulous buyers were buying his models, grinding off the "R", and then offering them for sale as originals. Eventually, Dick just gave up, which means that not all replicas from his company are marked. Dick died about 10 years ago, and his second-in-command, Charles Fleming, acquired the business and expanded it. If you want to fill in a gap in your collection, or get a model of a plane never produced by the military, Charles is a great source.
Some other things to keep in mind: Original models were intended to be viewed from ~35' away. That's about 1/2 mile, to scale, and was the effective range of the weapons of the era. US models have control surfaces and canopy markings, unlike UK models, but there was no need for that level of detail. Anytime you see a model, like those gray ones you mentioned, which show panel lines, rivets, and other detailing that would normally not be seen from a distance, you know you are looking at some relatively modern recreation, not something from the period.
A wartime model that is painted gray is another anomaly. Gray models didn't come out until 1948, so there would be no need for a gray Betty or a gray ME-109 (both wartime planes), to name a couple of the recent models offered for sale, to be issued by the military in the postwar era. The models are nice, and look better than the originals, so they have a place in the collecting pantheon. Just don't confuse them with military training models.
Cheers! -- Bryan