This may not add to the plethora of shopping advicee out there about Singapore but having lived here for 4 years with a constant flow of house guests you may find the following useful. 

1. Have a strong understanding of the product - brand, model and price - other wise you could pay twice what you would pay at home ie do a currency conversion.

2. Before you start bargaining (at Sim Lim or Lucky Plaza you must bargain) - determine whether the deal includes GST. There will be assurances that you can make a claim at the airport but this does not always work. Understand the terms and conditions of the GST refund system before you assume you will get one.

(Bargaining tip - try a few stores to get a feel for the rock bottom price, if you think you have got the best price, see if you can negotiate for inclusion or deep discounts on some wanted accessories that usually have higher markups - for example, cameras may not come with memory cards. In one case a friend thought they got a great deal on a high end SLR only to find it did not include the lens!)

3. Always determine whether it is a cash price or credit card price. Some vendors may charge upto 2% plus on a credit card transaction. If you are putting it on your credit card, know what your bank will slug you on conversion ie rate of the day plus a 1-3% conversion fee. It may add upto 5% to the cost which will kill the bargain.

4. For a mobile phone, find out if it is unlocked - easiest way to guarantee is to put your foreign SIM in. This will also give you a chance to see if you like the display, touch etc and whether the default language is the one you need. For example, cheap Chinese look-a-like brands will not have the original makers software and are likely to have Chinese as the default language. The alternative language options are poor and limited. That is, if you need menu and instructions in English - not everything will be in English and everytime you turn on the phone you will need to change the language option to English (ie always defaults to Chinese).

5. Check the charge plug. - European, USA, Asia, Australia - you may require an adapter when you get it home. Get one included in the price. Further, make sure the item will recharge on your home country voltage without converters etc.

6. Ensure you have a world wide warranty. Many products are sold without warranties and can become a costly paper weight when you get them home. on any Chinese look-a-like products, ignore warranty promises, they will never eventuate if you have a problem.

7. Finally, have a strong understanding of the product - brand, model and price - other wise you could pay twice what you would pay at home.....and yes that is a repeat of the first point!

There is an online article available here to help enlighten & educate those intending to shop at Sim Lim Square or Lucky Plaza.  This article will probably help minimise the chances of you getting ripped off.