I have not researched this specifically for appliances, but you could try motion alarms; attaching the appliance so it requires tools to remove; not putting appliances in until ready for the sales cycle and then using the mag key MLS type lockbox (it automatically verifies who enters and when, keeping a log of accesses); having the property alarmed (many alarm companies now allow you to assign different codes to different people so you know who shuts off the alarm).
Just some ideas. I know there are trackers, but the one I know about is generally built into the equipment (such as ocean shipping containers and the like) and to my knowledge are not yet mass market.
I recently had an expensive new regrigerator stolen out of one of my remodels. So I got to thinking that I could buy some battery powered GPS tracking device and hide it in the appliance. I thought someone else might have already researched this and could give me some feedback.
ps: I really don’t care if you don’t put appliances in your houses, or that you offer appliance credits at closing, or that you bill your insurance company.
I saw a ‘cops’ show once, where they found a big commercial aircompressor in the thief’s garage, because the owner had put a GPS onto it. But that was a 10K piece of equipment. I don’t know, if it would be cost effective.