While I can understand that you would want to trust the person you are buying your supplies from, you really need to put a digital thermometer probe on that heat pad, then tell me its low.
I have heard CRAZY explanations from pet store sales people that just want to get you to buy their products. If they do not carry thermostats (which very few pet stores do) why would they tell you that a product they sell cannot be operated safely without it's counterpart - which they do not sell. So they don't care and tell you it will work fine without it, which is entirely false.
There is a HUGE difference measuring the temperature above the heat pad, and directly on it, where your bp's sensitive belly rests.
You can choose to use products however you please, but in all politeness, please pick up a digital thermometer and find out for your self that your UTH is very likely too hot.