More seriously, the 'matching industry' has two flavours currently that can make money. There's the geographically diverse Uber model (I want the single nearest transport wherever I am) and the Tinder model (I want all the orifices near me).

For a dog-walking app (or many others, such as say house-cleaning) - you want an introduction to people locally, repetitively. Once you're happy with what you got through the app, you don't want the app.

Maybe what "Wags" should focus on is the broader scope of "I want a local tradesman to do something repetitively".

Provide introductions, take a nominal fee, allow end-user to change if they're unhappy (and take a very low fee for all the happy people)