I had a friend who tried a similar idea. She offered a subscription service where she would go to people’s houses twice a week and scoop their back yards. Her rates were higher than this. These rates are not viable. At $0.25/scoop, with transportation costs and assuming your time is worth something, there is no way to make this viable.
A human earning $8/hour makes $0.13/minute. In other words, you would need to scoop 30 times per hour in order to earn this much. Even in the busiest dog park, this would be a challenge. And of course the company will take a piece of that $0.25/scoop.