Please reconsider the conveyor belt idea.
While this idea might seem fair since you see what item you currently get, it's pretty much just an advanced gacha machine. People will still pay for the chance that the rare or item they want appears on the board.
If you don't ban it, atleast make restrictions like "board gotta cycle to next item atleast once every x min" and "a min of 2 mins needs to have passed before it cycle to next item"
Reason for the first is to avoid having to play it like a gacha machine to get the item you want
Reason for the second being that if more than 1 person are paying the board at the same time for the item that is currently there, they should all get that item and not only 1 while the rest gets something random