on how much money they have spent on the back-end part of the website.
If you have enough money you can have a system that will track stock movements almost instantly, but you have to integrate the whole company system from ordering incoming supplies to dispatches to customers and it will be expensive. Most companies will take the option of daily or weekly website updates. Having several branches further complicates the problems as the stock may be scattered around the branches and need to be dispatched from any one of them.
The company that I work for has to make this decision soon and it is a hard one to make, I want to go for daily stock updates, my MD would like to run live stock but doesn't like the cost of integrating the stock/accounts system to the website that was designed and run by a different company.
Unless you have a lot of money to spend on the back-end systems you will never have a good stock indication on the public bit of the system. Even the best system get thrown by human error sometimes, it only take a store-man to put the stock in the wrong bin or enter it wrongly on the computer and it could be months before it is found!