If I was using a service like this regularly, I don't believe I would tip on a regular basis, especially if there is a delivery fee.
This whole tipping thing has gotten out of control. Being a regular paying customer is keeping them in business.
If I had a lot of heavy things, or many steps or other difficult circumstances and I could afford it, I might consider it appropriate to tip.
I think a lot of people with disabilities and the elderly will be using these kinds of service more and more in the future, and often, they don't have a lot of extra money to do tipping for every service that they have already paid for.