What is a freely spinning wheel?
Of course, you should be able to spin the wheel by hand, but beneath the brake, bearing and transmission can apply lots of drag. My rear wheels do about 1.5 to 2 turns, my front wheels not more than half a turn when I put them in rotation by hand.
While it's the same for the front wheel of my mother's car, its rear wheels seem to spin forever.
It's best to compare the left and right wheel to get an idea about the expected drag, furthermore, one can compare the drag before and after removing the caliper as well as after removing the pads. (Pads alone can be seized due to dirt / corrosion, too)
Temperature also gives a good hint on whether a brake is seized or not. Highly seized brakes produce lots of heat, slightly seized ones still a little.
But again, it is not easy to judge if a wheel is slightly seized, as the temperature depends on drive behavior, weather and the car itself. And the bearings and tires also produce some heat.
It is again best to compare right and left side.
In my experience, I once had a highly seized brake in the rear which still wasn't noticeable while driving. But after, I could feel the heat on my skin when standing away one meter from the wheel...
I now have a infrared thermometer and measure temperature of wheels and discs from time to time.
The second time I had a highly seized brake (front), the wheel had a temperature of 100°C (210°F), and the disk of nearly 300°C (570°F) after driving 120-140km/h (75-85mph) for 30min plus driving home at low speed for 5min. The seizes brake was only noticeable while driving at that high speed, as it started to make noise and the car pulled to the side when braking. It was not noticeable when driving in the city.
However, don't be too paranoid. When my rear discs and pads had been replaced, the temperature difference between the discs was 20-30°C, but as the brakes broke in, the temperature difference decreased and now is in the order of 5-10°C.
My left/right discs now differ about 5-10°C in temperature, but when I had my rear discs and pads replaced, both sides differed by about 20-30°C.