Why not have your Book delivered to your doorstep (via Singpost)?
It takes only about 1-2 days
plus, its' cheaper than taking a transport specially to collect the book. For example, if you took our MRT for 5 stations, it would cost > SGD $ 1.00. Getting there and back would be > $ 2.00. If you had to transfer a bus, then it will definitely cost more. Not forgetting the amount of time spent travelling.
Unless your seller / buyer stay near you OR you have a car OR you're on the way. It will might cost you more time and money to personally pick it up. Well.. this is just the personal option of Bookfishing.com.sg. Anyway, here the postage rate!