Do not you think that the owner of the pet store will spend too much time on the implementation of your proposal?
It won't take more than a hour to set up everything he needs. It only requires him to create a channel and increase the inbound capacity (to receive payments). Creating a channel requires 5 minutes. I have shared tutorial above and you can check that. It's not that much of hard as you are thinking.
Lightening payments look great! I could even sell the system to other shops?
Your questions aren't clear. What are you referring to?