imagine a "purchase" command but it works on any npc, objects using the price set in the inventory tab of items.

would like someone to give me an idea on how you would make it.

There is a tutorial here:
http://docs.textadventures.co.uk/quest/shop.html

If your vendors move around, it will need to be adapted.

basically, i'm just looking for information on how to buy anything from any npc's inventory, even if that npc can move around freely. Basically, walking up to a stranger, and trading.