Since there are a couple of douchebags keeps buying all of the items and selling them in the market for a higher price, there should be an automatic restock, where when it will be sold out it will restock within one hour.

Shop restocks on the 1st of every month. Changing the time wouldn't fix the problem, people would still buy everything to try & profit from it; they'd just do it more often.

There are already a few other suggestions regarding the market & keeping it under control, they would make more sense in the long run.