*You cannot put items inside containers on to a Merchant. The container must be emptied before the Merchant will accept it.
*The inventory limit for a Merchant seems to be about 50-55 items?
*Simply removing items from the Merchant resets the 'Last Sold' timer (a bug?). So in practice it's not hard to stop the Merchant from packing his/her bags because he hasn't sold anything. Just visit once a month (28 days?) and remove an item, then replace it.
*Putting large numbers of low-value items on a Merchant is hardly worth the effort as you have to set the price on each one individually, even if they are all identical.
*The "Manage Prices" window is slightly better than Set Price, but not much.
*Dismissing merchants (to store them or move them around) seems to have no penalty as long as you remove items and money from them first. A dismissed trader's items and money disappear.
*If the trader has no interaction for a month (28 days?) or is wizkilled, he is dismissed, but he can still be placed again as usual.
*Selling a merchant contract to another player is not difficult. Just dismiss the merchant and trade the contract to another player. Again, there is no penalty as long as you remember to remove the money and items before dismissing them.
To Investigate: