While many shops closed over Lunar New Year, most supermarket chains and convenience stores stayed open. This made sense, as the fixed costs, like rent and equipment, were there already. During the holiday, smaller businesses faced higher variable costs, such as wages, which might be as much as double. To get around this the employers pass the extra costs on to the consumers. For example, some Chinese restaurants charge 20 per cent on top of the bill for the first three days of the New Year, to help pay the additional wages. Customers usually accept this as a matter of practice and tradition. But when you visit the supermarket you know that you can still buy items at the cheapest price. You will not be charged extra even if shopping hours have been extended. However, did you know that the supermarket has other tricks to make more money from you without you being aware of it? Supermarkets have researched customer behaviour over the years. They have ways to tempt you to fill your trolley and empty your wallet. If you take a look at the floor plan of a supermarket, you will have some idea of how it works. For instance, say you need to buy some daily items for your mum, like bread and milk. These commonly purchased items are usually placed at the back of the store or in a far aisle, forcing you to walk past other tempting products on your way. As you walk through the aisles you might pick up a bag of potato crisps. Then you may stop by the magazine stand and end up buying a paperback book. Finally, before you reach the checkout counter, you grab some chewing gum or a packet of sweets. All these items were not on your mum's shopping list. The old sales trick - two-for-one or buy- one-get-one-free - aims to get rid of old stock. Remember, don't buy more than you need. The one-stop superstore offers dry-cleaning, copying and printing services. Once you enter the store you will be tempted to use more than one service. And did you ever realise that the music and shopping tips they play at supermarkets are a way of luring you to buy more? So the next time you step into a supermarket, think about how to manage your mind. Dr Sze is the president of the Society of Registered Financial Planners. If you have a money-related question, send it to yp@scmp.com with Money Matters as the subject