Trappers looks will fool you, some of the best are a lawyer and a Dr. in the off season. Like picking out the anglers in a crowded office complex. A couple well known trappers are so fat that you would think they never leave the couch and one I know of is one legged.
For the most part cats feet support their weight so well that they don't leave many tracks, often in snow a big cat's track will look kinda like it was made with a lady's powder puff, no real distinguishing characteristics. A better indicator of species is often the print placement pattern if a trail is visible. Is the trail wandering, staggered, straight line, are prints overlapping, overprinting etc. and so on. A red fox trail in snow is distinguishable from a domestic dog's trail at a distance or in a drive by; but a single print might be hard to tell.