Okay...so let me get this straight... You want to place a cooldown on something no one uses anymore. Um...what? The stalls are a flawed idea which I noticed very quickly. Back during the days of no item search, I always found myself never checking any stalls. Why? Because you literally are going a little out of your way, making an effort to target them specifically, only to find out they're selling exactly what everyone else is selling. Everyone else, who are all clustered together and easier to sift through. Now that there exists an item search, the stalls are made even more useless. Also, no amount of fair incentive will make the stalls work.
And another thing: Cooldowns are the poor man's way of solving balance issues. If balancing is too difficult without the addition of cooldowns, then more variables need to be added or variables need to be removed.