Welcome to the forum! I hear you about the rat race, but there is a lot for you to think through. The 'rat race' is providing you with steady income, probably health insurance, sick days and/or vacation days, a 401k or other pension plan and probably some other perks that just don't come with Independent Contractor status--which is what you are if you are a shopper.
Do a budget of what your minimum cost of living would be. Figure that an average mystery shop will provide you with $12-15 in fee plus value of the reimbursement. How many shops per week will you have to find to cover your minimum cost of living? For most of us, mystery shopping is a supplement to another source of income. (Spousal income, Social Security, a 9-5 job, retirement savings, etc.)