Thermostats are ESSENTIAL in keeping snakes in a healthy way. Any individual or shop that chooses not to use them is either unaware of the risks, or chooses to risk the health of their animals for the sake of cost. Un-statted heat sources can get very hot.
There are also other problems with not using a thermostat, even if you happen by chance to get the correct temperature in the viv. What happens in the Summer months when the ambient temperature rises by 5-10'c? This means that the viv temp will also rise, and there is no way of reducing it. What happens if your snake develops respiratory infection and you need to increase the temperature in a controlled way by a couple of degrees for a period of time. Again without the thermostat you do not have the control
over your snake's environment. In my view when we buy snakes we take on full responsibility to provide the exact requirements they need to live in the best health possible. By not having a thermostat, you sacrifice that level of control and compromise your ability to meet these requirements. For me that is unacceptible.