This is a simple mod that allows admins/moderators to view the inventories for players by using the /inv <player> command. I'd previously written an even simpler version that uses formspecs, but there is a bug in the Minetest engine that doesn't allow it to work for other players' inventories. So, in the meantime, this is a text version.
Download: https://github.com/thefamilygrog66/inventorycheck/archive/master.zip
Browse code: https://github.com/thefamilygrog66/inventorycheck