You can have as many Bobs as you want, which can all function at a very low cost and compete for users with low fees and high service quality. I can easily imag

You can have as many Bobs as you want, which can all function at a very low cost and compete for users with low fees and high service quality. I can easily imagine registering your transactions to tens of different service providers, making it quite impossible for Alice to pay them all of (or even know who they are).