Using drones termial give you what you purchased instantly but when the drone comes back it also give you what you purchased so you get double the items.

I recently played on two servers where I repeatedly used the drone marketplace to purchase items from a vending machine that was customized by this plugin, and I don't recall seeing this issue, so it's probably due to 2 plugins on your server handling the transaction at the same time. Do you have any other vending machine plugins installed?

Merged post

Update: I tested the Vending Manager plugin and saw that it is causing the behavior you are seeing where the item is instantly given to you. That is a bug in that plugin. If you update to Vending Manager 0.2.10, the duplication bug is resolved, but the instant giving is still an issue.