I don't count them as profit, but more as a discount against things I'd buy anyway. I rarely end up in the "plus" column on a flat-fee purchase shop, so there's no profit. E.G., I did a Super Shoes shop over the weekend; spent $45 for the shoes and will get a $20 fee. I figure it as a $20 discount if I keep them (not sure on that yet).
I'm always over the car-wash reimbursement because the location charges more for the required package. But I figure paying $4 or $5 for a full car wash is a good deal.
If I were to do, say, a flat-fee dining shop where I got that $100 fee regardless of expense, and spent $85, then, sure, that $15 is a mathematical profit, and I'd feel that it was, but I had to work for it, so it's not like it's free and clear above the $85.
I learn something new every day, but not everyday!
I've learned to never trust spell-check or my phone's auto-fill feature.