@Roxanne SB
The vast majority of shoppers do this as a side hustle. There are a very few who mystery shop as their primary source of income. Some are active on this forum. I do this as a significant side hustle, but have no intention of replacing my full time job.
If you want to do this full time, start by working to maximize your shopping income by, primarily, earning money more efficiently. As you do so, you'll want to greatly expand your relationships with MSC's and make yourself fully aware of the breadth of opportunities for you in the industry.
There are quite a few threads on this board about doing this. Some very experienced shoppers have shared a lot of their strategies for earning good money through mystery shopping.
Hard work builds character and homework is good for your soul.