To buy or sell, I notice there is one in Peninsula Plaza on the second floor. It is not in the main foyer are but in the back area shop units. Just a few doors down from EastGear shop.
The same type of shops that buy and sell are at Sim Lim Square and again not facing the main foyer but those more quiter shops facing the outer parts of the building on the 4th floor.
My opinion is that you will never be able to get a good price for your notebook as they will bargain you down and belittle your notebook as way old or technically too backward as technology is moving so fast forward..blah blah..and then they will up the price to get a good selling price for them but the good thing is...you dont have to worry about giving personal warranty or worry if something goes wrong with it, you have to take it back and return the money to the buyer. The shop take all the risk and servicing for it. For me if I was selling my notebook, I would sell it to a buyer myself and get a better deal for it. BUt of course you have to be sure you know what you are getting yourself into.