Only the leader of the clan can do this, at least one day should pass after the previous sale, and the counters, of course, should be full of expensive goods. 
Everything's ready, but you still can't start the sale? Well, let's not tire you with specific formulas, the only remaining obstacle there - the quantity and quality of the goods themselves. You just need to increase the number of expensive goods on the counters. If there are still not enough items for sale - try to increase the clan itself by accepting new sellers ... we mean new players, of course, players! Right. Rookies will also have to list expensive items for sale. Then you'll certainly succeed! :)