If I'd steal a phone, first thing I'd do is take the battery out. Right after the job. Second, do a full wipe using Odin or similar tools. Third, reflash the firmware. As long as the device I stole is not an iPhone, the phone is now completely under my control. And for what its worth, to avoid tracking it is iirc possible to put in fake IMEI, BT MAC and WiFi MAC addresses. No one compares these anyway, and e.g. a swa…
The crossover of people who know to do all that and people who steal phones is very, very small. People who tend to get in to petty thievery are not the type of people who have the technical skills or even the forethought to take those precautions.
If you're doing this on "professional" level, likely the guy picking up your loot will have told you at least about 1), alone to reduce the risk of cops tracking down the merchandise. If you proved to be not at least totally bananas, he might also tell you a bit more - the less time the stuff is in his hands, but in yours, the better for him.