Migrated from: https://dev.bukkit.org/projects/shopkeepers/issues/416

Originally posted by mat41997 (May 30, 2016):

to stop capitalism on my serwer : O

I am not fully sure what purpose settings like that would have. Maybe you, or someone else, could elaborate on what the effect of this would be and why it would be needed?

I would like to reinforce a specific currency and that currency can be bought with diamonds, however, I would like to stop people from just straight using diamonds. So what I was suggesting is, a blacklisted item to not be used as currency. For selling shops, players wouldn't be able to select diamonds and for trade shops diamond could not be used as the trade value.
Setting that in the settings wouldn't change anything to whoever would like to trade as it currently is, but it would add a new layer of options for those who want to create something more elaborate, such as custom made items to work as currency.

For selling shops, players wouldn't be able to select diamonds and for trade shops diamond could not be used as the trade value.

You can already achieve the selling and buying shop portion of this by changing the currency item inside the config from regular diamonds to your special item. See here for an example on how to specify custom item data inside the config: https://github.com/Shopkeepers/Shopkeepers-Wiki/wiki/Configuration#example

Regarding preventing the use of regular diamonds in trading shops: If you want to force the use of your custom currency item, it might make sense to disable the trading shop type altogether for your players (by removing their permission to create this type of shop).