As Gavin says the term "G Scale" is a bit of a misnomer. It basically can cover anything that can run on LGB's (and the myriad of compatible makes) code 332 rail/45 mm gauged track systems - so models anywhere from 1:13 - 1:32 are made to run on it and can be sold as "G Scale" by some vendors.
Even from the same manufacturer there will be variations in the scale of the models they sell to suit the subject matter to make it "look right" for use on the 45 mm gauge track systems mentioned. They also may not be scaled proportionately correctly either to overcome other considerations for operation. If you want advise on scale compatibility then it would be helpful to know what type of loco and stock you are thinking of buying or what you want to match it up to. What sort of railway subject matter are you interested in ?
There is also another fly in the ointment, that here in the UK at least, a quite predominant sector of the garden railway hobby is the 16 mm scale (1:19) - Those who indulge have locos and stock supplied by manufacturers that can mostly run on
both 32 mm and 45 mm track gauge systems. You can see where the confusion can set in.
My understanding is that most "collectible" farm equipment models are built to either 1:16 and 1:32 scale - is that what you meant by "32 mm" when referring to the tractor you bought ?
Here is a Britains 1:32 scale item. It would be ideal for use with any, what is termed "Gauge 1" locos and stock (also 45 mm gauge but more likely to prototypically correct in their representation than most referred to as "G" scale), G1 is (mostly) 1:32. It would also be passable for use with makes like USA Trains, Aristocraft (which is what I did ) and some LGB models of US standard gauge prototypes, which are nominally 1:29. It would though look small when offered up against Piko's models of European standard gauge prototypes, which are scaled nominally at 1:26. You can see the problems.
Max
P.S. It's for sale as I moved away from that scale to 1:20.3 and 1:19. I now buy 1:18 and 1:16 vehicles to "match" into those scales.