Not to start an argument, but I wouldn't do that either. For one thing, a few minutes in the oven won't do anything but heat up the first 1/8th of an inch of the soil pile. It takes a long time to heat to the center of soil. Also, heating soil like that can cause it to become toxic. Its normally steam sterilized.
IMO, if I found myself having to go through sterilizing soil, I'd just buy better soil. And yeah, here in the north, especially in the spring you have to be carefull you're not buying last years excess inventory. No faded bags, and nothing wet.
<playing devil's advocate>
If that's the case, why do people do slash-and-burn farming? I know the idea is to create ash to fertilize the soil, but burning wood/plants/debris directly on the soil itself would substantially heat the first couple inches of soil. If toxicity was an issue with the method, an estimated 250 million farmers worldwide who use it would be cropless. If you need to sterilize it, as long as you only do small amounts and keep the heat below 200 degrees, you should be fine.
I understand what you're saying about buying better soil, but sometimes it isn't possible to obtain better soil locally. For instance, where I used to live, there was one nursery/garden center and it closed during the winter months. The only option for soil was either purchase it online(couldn't wait / couldn't afford the markup) or buy the crappy stuff at wallyworld that had been sitting outside since summer.
</playing devil's advocate>
However, if it were marijuana plants I was purchasing soil for I would buy the best I could find/afford. If MG is the best I could find/afford I would make sure it was the best bags of MG I could find.