Here's the ask.
General.
1. Available in central locations that let you search for items, such as the crossing plaza. Even if it just searches the look.
2. Pagination
3. Lists all items currently available in trader shops
4. Allows purchase (with fees) outside of the normal shopping window for that shop, and in other provinces.
5. [future addition] the ability to place buy orders (it won't actually sell you the item, but you can leave a public note (for a small cost) saying how much you're willing to pay for an item. Traders can then read it.)
6. [future addition] trader magic (mind reading) that lets them read the market board from afar (specifically the buy order portion). Uses the same distance mechanics as teleport.
7. [future addition] allow for auction-like mechanics. List an item for a range, and the highest bid at the end of the time-period gets it. Higher fees for longer postings.
Usage.
1. Indexed with a buy confirmation. ie: A) search, B) type buy 1, C) type buy 1 confirm. If the item is gone between A and B then it shows a different item. if the item is gone between B and C then it won't let you buy.
2. Uses a "runner" system to get the item. This is an internal check. The runner takes your gold. Goes to the place (invisible). Tries to execute a buy on the item. If it doesn't exist then it'll return your gold and issue an internal error report.
3. To buy an item, you need the required amount of currency in that denomination on your person. So you need 10,000 lirums to buy a 9 gold item in haven.
5. There is a fee (maybe 20%) for buying an item when the shop is closed. This is charged to the buyer at the time of purchase.
Reasoning.
There are too many shops in too many provinces to go browsing. With critical tools like this (https://dr-scripts.firebaseapp.com/) shutting down, it makes sense to bring that in house for traders and non-traders alike.
