There is two current methods to force the restocking of a shop.

1) Press Select and wait for a total of 48 hours.

Pros--
Refills everyone's stock

Cons--
Wait time in game can massively increase.
NPC can walk away or go someone forcing you to wait longer.
Since NPCs and random events occur, you may run the risk of your shop keeper or one nearby being killed by a random NPC (Thief, Ect...)
If game crashes during a wait you lose everything you have just spent your time on

2) Buy/sell merchandise. Save the game. Kill the merchant. Reload the save.

This forces the shop owner to reload their inventory.

This is extremely effective for the Kajjit in Downstar with the hidden chest. Since they pack up and leave every so often and sometimes don't re-appear for a while, you can use this to instantly reload what is in the chest while keeping the contents you got.

Pros--
Refills the target merchants inventory.
Fast, Effective, sometimes quicker and more reliable than waiting.
Ensures you keep your content in case of a freeze/crash.

Cons--
Only 1 merchant at a time.

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I have done the kill/reload and have found that when you are dealing with someone who can get up and vanish and they have something you want to buy multiple times, that method works best.

If you are in town, set the time to about 1pm and then wait 24 and 24 to refill everyone. Very quick if you have a lot to sell.


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Just felt like sharing the methods to anyone who didn't know.