From the NannyMUD documentation

LAST CHANGE

2001-10-06

RULES

NAME
        shop - rules on shops


DESCRIPTION
	The shop in the village is hereby declared the upper limit on how
	good a shop is allowed to be in the rest of the game. Shops buying
	things must be approved, those only selling things might need to be
	approved.


	SHOPS SELLING THINGS

	Sell only a limited amount of things per reset, and sell them on
	general terms like 'good', 'average' etc. instead of 'wc 17 sword',
	'class 4 shield' and so on. Of course you can sell things on the name
	alone. Charge the players at least 2*query_value() of the item you
	sell.


	SHOPS BUYING THINGS

	Shops buying things need approval, and in order to stand a chance of
	getting it, they have to use the shop system under /std. Your shop is
	allowed to pay 90% of the items value only, up to a maximum of 900
	gold coins.