Plugin Help Essentials Eco Sell Sign

Does anyone know how to configure a sell sign so that you can sell items even when you dont have enough of it. Lets say you have 32 seeds and a seed sign allows you to sell 64 seeds. Is there a way to configure essentials so that you can sell 32 for half the sell amount (Ive seen this done on other servers)

 

@FourthRobin Are you sure the other servers have been using Essentials sell signs? I’ve never seen this done before.

 

Hmmm they use the same format but I guess perhaps they might not use essentials. Thanks for the reply though.

 

@FourthRobin Could be a custom plugin made to look like the Essentials sell sign because they like the look of it? Just guessing here.
If you don't care about the plugin doing the work or the format then i could recommend this plugin:
https://dev.bukkit.org/projects/chestshop
I've been using it before because of the ability to sell items even if you don't have enough. (Sounds like what you are looking for)