18-200mm no USM btw, only IS.As for where should get DSLR, a thread has listed a few reputable shops, include, but not limited to Cathay photo, MS color, TK foto, Orient photo, PArisilk, SLR Revo, etc, etc.
If you have the money, EFS18-200 is a good choice, a few CSer quite like this lens. IS, USM.
check everything included in box. Check if there is no physical, visible scratch. try to snap one photo if possible. sometimes battery not charge so not possible. But a few shops allow you to try at home and 7 days 1 to 1 exchange.
Check if it Sg warranty, the warranty card chop with shops stamp, and receipt.
28-200mm have USM, but no IS.