In no way is it just Corporate pet stores that do this. I have a decent, non-corporate reptile store near my home town called Anamalia, and I consider them to have great products, and in general, informed sales-people, but even they do not carry thermostats and say that a UTH is fine uncontrolled. They also recommend a lot of products you don't need when someone buys a new reptile.

Anyway, I'm not trying to tell you not to trust any pet stores, thats not as important as being sure your snake is safe. It is good to hear that your UTH is not closer to 110 degrees, but a thick layer of substrate in no way will stop your bp from burrowing under it. And if you have never seen your bp burrow beneath it, well O.K but it can happen, so why risk it? As mentioned, if you can afford a thermostat, it is the sensible thing to use Do you honestly think your UTH will never go higher than 101? It can and likely will.

Were just trying to help, not bash your set-up I promise.