You are responsible what happens with the plugin after you download, therefore, if plugin is leaked or redistributed and it's registered under your name, I am allowed to remove you from buyers list without a warning. I may be obligated to report you on SpigotMC.
You may not redistribute plugin, in any shape or form neither it's code or parts of it.
You may ask me for support.
No refunds, as one does not have a right to get a refund for such digital item, because you have been gained access to it instantly and may have used it.