That’s not really what agile is about. It is about early feedback, so yes the customer might see an incomplete product. This is similar to watching a bespoke house being built. As long as they wear a hard hat, it’s ok for the client to inspect the footings.
This is exactly why I hate Agile garbage. Just about everywhere I've ever worked has applied "agile" and all it's lead to is them building crap software quickly. I'm all for releasing early and often, but not "in whatever state". Have some pride and build good, well tested software.
I’m not sure from the poster’s description it’s just a hobby project. They evidently want to charge their customers money, so there needs to be some level of quality in order for that to have a chance of working.