A few tips that may help:
With only a few exceptions, Yanmar's older grey market machines will have four digits and possibly a letter after a "YM" prefix. Eg.: YM1300, YM2000D, etc. More recent Yanmars have an "F" or "FX" prefix, followed by a two or three digit number, with a possible "D" suffix. The D indicates a four wheel drive machine, and X signifies the machine has a Powershift transmission instead or standard gear drive. Newer is not better, really. The F/FX series are nowhere near as well supported as the YM series. Think 1960s Mustangs vs mid '70s Mustangs.
Grey market Yanmars are generally very similar or essentially identical to domestic machines. Engine rebuild parts and many other parts of that sort are available, along with some gears, castings, steering boxes, etc.
So far as I am aware, all Hinomotos are grey market, whether in Canada or the US. They did build some tractors for other companies, such as Allis-Chalmers.
Most Isekis are virtually all grey market. I say "virtually all;" because there is, technically, a dealer in the US. They are in Hawaii, and apparently sell current production Isekis. The odds are overwhelming that a used compact Iseki is a grey market unit.
Mitsubishi/Satoh made an array of machines for the US/Canada market and for their domestic sales. They are very similar. My Satoh ST1440 is the essentially the same as a Mitsubishi S373D Beaver III. (Technically mine says Kumiai on it, but it is a Satoh.) I think all D-prefix Mitsubishi machines are grey: D1500, D2000D etc. Again, D signifies four wheel drive. Two or four digit Mitsubishis are grey, I think, while three digit machines are US market. MT16 and MT2001 are grey. An MT180 is a US market tractor.
Kubota has the widest range. The B6000 was produced for both markets. The L175 and L1500 are close cousins. Others are essentially identical, but renumbered, and sometimes differences are visually more distinct than mechanically:"The B6100 and the B-6001 tractor are- with the exception of tire size, the language the warning and operating decals are printed in, and the direction in which the throttle advances engine speed-identical tractors. "
(From Service Department Vic at
OrangeTractorTalks - Everything Kubota - View Single Post - b6001)
Of themselves, grey market machines are just fine. Sometimes they have been repainted and are presented as "refurbished" or some similar term. Generally the advice is to avoid these tractors at all cost, since they are sometimes cobbled together with parts from incorrect machines, then painted nicely. A used refurbished unit is generally safe, since the previous owner had the tractor, and presumably has resolved all the major errors or shortcomings in the machine.
If you post some specific models, we can likely help you.