How do you know what a good restock is? Do you have a list to watch for or what

I use Jellyneo for a basic reference on prices, BUT, Jellyneo has it's prices suggested by the players themselves, so make sure you click on "view full price history" so you can see if what the price is over a long time

Most guides say to watch for items worth 5,000np or 10,000np exactly, as they are usually profitable in a shop such as books or food, 2,500np items are usually profitable as well, but only a few hundred nps at best
most items worth random amounts of NP are worth less than the cost, so stay away from those

I like to check any food store and the toy store, almost all 10,000np food is very profitable, as a lot of them are UBs, some 5,000np food is profitable, but only for a few thousand
and the toy store restocks Goodie bags and treat bags, which can sell anywhere from 40k - 1mil, and they only costs like 3k to buy from the store (very good choice to start with)

after awhile you just start to know what to buy and what not to