The Grand Exchange 4 hour rule links in with solo and flip merchanting hugely. The biggest reason is because it only allows you to be able to buy a cirtain amount of items every 4 hours. This can give you an advantage or a disadvantage because if the item has a high 4 hour limit, it is easy to stock pile the item quickly and also finish buying before the Grand Exchange updates, therefore giving you an advantage. If the item has a low 4 hour limit then you will not be able to buy many items very quickly therfore a disadvantage.
Therefore it is highly reccomended that you make sure the item you are about to invest in has a high 4 hour limit by checking the list on the page 'The Grand Exchange'.
