Thanks for the feedback.
"why not just leftclick to interact with good things or attack bad things?"
For a couple of reasons:
1. I eventually want there to be more than one action for some game objects so I need a way to have different buttons do different things.
2. I liked the idea of click always attacking to avoid a scenario whereby you are trying to attack and end up doing 'good things' instead. Basically I liked the idea that left click is always unambiguously attack.
Having said all that you are not the first person to say it isn't exactly intuitive, nor are you the first person to kill the shop keeper kek. It looks like I will have to give my control scheme some more thought. In the meantime I think I'll make the shop keeper be a little tougher.
"Second Run I couldnt interact with him again, maybe because I killed him in the first run."
Yikes, this is definitely a bug, thanks for pointing it out!