I see somebody say set the item -> gold in shop edit, but that way so limited

But now I found a way can sell the item I want by double click, but there’s a problem, I don’t know how can I do that althought I did it …

But now I want all shop can sell item like the petshop, anyone help?

This is the petshop, you can see in the chatting, I sell successful

But in the weapon shop