Because it's against the law to use common sense and let anything be simple. And forcing a third person into the transaction deters any "special friends and family rates."

Yes I believe it is all about insureing that all moneys are accounted for.

To employ more people.

Just so they can make the shopping experience as unpleasant as possible so you never want to do it again.

E.g i have a shopping mall or supermarket which i rent out a part of that store to you for selling your products and you pay me by number of goods you selling , comision or percentage

This is also common in over developing nations such as Brazil....never really figured out why they do it but thought the 2 most likely reasons were to prevent one person stealing the money or some kind of government policy to employ more people

Some malls and shops use a central counter because of the way the rent structure is set up. In scenario number one, one person or company owns the entire retail space and they sub-let sections of the space to different shop keepers. The central counter is used for 2 reasons: First, so that the owner of the space can be sure which stalls are making money (so they can kick out ones that aren't profitable) and second, the stall owners usually pay a percentage of sales either on top of, or as their rent. This is an easier way to keep track of the sales and make sure there isn't any unreported sales that wind up in someone's pocket.

The second scenario is that one company owns the entire retail space and they themselves actually run all the different shops, so it makes it more convenient to just have a central payment area. It also is an old form of product tracking, so they will have a fapiao to see what store sold what, which salesperson made the sale, and what product sold for what (as you can often bargain at these places - they want to know if Salesperson Li is selling things too cheaply, etc.)

So either way, it just makes the accounting easier at these places.