Betsmarie, have you read the Sticky thread on taxes in this section of the forum? If you haven't read the Stickies up at the top of this page it would be a good use of your time.
Quick answer: You add your fees and reimbursed expenses together for total income (the total mount the MSCs paid you). You subtract what you spent on the reimbursed items as an expense. Your mileage is also an expense at a set figure per mile (haven't checked the number for 2014 yet but it's in the ballpark of 56 cents a mile). You have to have a written accounting of the mileage, the miles you drove, the dates you drove, and where you went and what you did. You can also subtract a certain amount for a home office if you have a dedicated area and meet all requirements. You can subtract any other reasonable expense that you incurred. Report your income on Schedule C regardless of whether your profits are $400.00. Your mystery shopping income, no matter how small, will be added to any other income you have (or if you are filing jointly will be added to the family income).
This is general information. I am not a tax preparer and I am not a tax expert. You should consult a CPA, an enrolled agent, or the website IRS.gov for detailed and accurate information.
Mary Davis Nowell. Based close to Fort Worth. Shopping Interstate 20 east and west, Interstate 35 north and south.