How do restocks happen in the torishop and how often do they occur?

1st day of each month = restock. Or the last day? I don't remember which one.

Some items get their amount in the shop increased (not all of them), so that the market will stay going (at least, that's what I heard) on the restocks.
I think (not sure) that TSAs (torishop admins) do the restocks.

This happens on the 1st day of every month.

Restocks occur on the 1st of every month.
I imagine restocks to be automatic.
If it's not that, then TSAs probably restock the items manually.

Are some items never restocked to increasse value?

I wrote a long piece of text which disappeared because of a connection fault, so I'll make this concise.

Prices of items are not raised to increase an item's value because the lower the prices are, more likely people are to buy them from torishop. The current prices have been found to be quite effective and there aren't really staff in toribash who would actively monitor what prices players are willing to pay for individual items, so no item prices are raised. The prices must be suitable in the sense that people want to buy items from torishop by which tc goes to toribot which is an account from which tc can be deleted and therefore tc's value raised, and furthermore people have to buy more tc with real money

^no facts here, just guessing with logic