They are hoping to attract shoppers who are looking to make such purchase anyhow. For instance, if you are planning to buy groceries and performing a shop will add an extra 15 minutes to your trip (including the report), the $15 reimbursement just might be very worthwhile. Car service shops can be a fantastic deal if your car needs work, too!
I love reimbursement only grocery shops. I cook food. I need food. I am going to buy it, probably at the store I am shopping, whether or not it's a shop. Reimbursement only shops are not considered taxable income. I do lots of different kinds of shops, so having some I don't get taxed on is great.
I also get a fee, as well as the oil change. And, if I use a coupon, that boosts the bottom line to me since I am reimbursed as if no coupon was used. Example: $10 coupon; $8.00 fee, $40 oil change. I paid $32 for the oil change but get still get a total of $50 pay and reimbursement. Super simple report.
No one is suggesting that you should lose money by taking reimbursement shops that cost you more, net, than the alternatives available.