How do I politely tell a client that walking their dog isn't financially viable for me any more?

Honesty is always the best policy, if the parking situation has changed you have two options. One charge the client for parking or two let them go but tell them why. You will also be doing them a favor as other walkers will encounter the same situation. Best of luck

I totally understand! I live in a city too and have stopped taking clients who live where there is no free parking. I either have to take the bus, which I don't mind but costs money, or pay to park. I agree with everyone else. Tell them the situation and they might offer to pay you more to keep you. You won't be the only walker with the same problem. Only someone who lives in the area wouldn't be paying for parking so even if you lose them you will be doing them a favor by bringing it to their attention.

I agree that honestly presenting this dilemma is the best approach. By telling them what's happening, they may surprise you and offer another solution (maybe they'll find a nearby neighbor who will allow you to use their spot for the time you're with their dogs - who knows, maybe they'll help network you with a nearby dog owner who also needs your services and can provide a space)

I know the question has already been answered but as a fellow sitter I wanted to throw in my agreement of Walt and Deb said. Definitely be honest. Most dog owners that hire someone understand that this is a job for you, therefore they should understand you expect to make money. I know those are hard conversations to have but I would definitely let them know. Personally I would take the approach to offer to have them make it profitable for you, if you like them and the dog. A simple, "I really love walking Bubba but I've noticed I've had to pay for parking recently. The rate you're paying does not include parking and I've recently paid more out than I've made. Going forward I will have to raise my daily rate to "x" to include parking. I'm open to other suggestions if you have them." You can see how they respond or you can add in the initial message something to the affect of "I understand if the increase to cover parking is not feasible and you want to cancel our walks." I'd probably leave that out of the first one. Unless you want to give up this client for whatever reason - in that case this is a good reason to peaceably end it. Good luck!