Question please~

[gigabytexx]

Hi, does anyone in here likes to shop anything in eBay ? Any tips on how to buy wisely in there?
I mean, if the detail said it's "Brand New" with the sealed package pictures included, is it usually true like that? And why do some of the items are being sold lower than the prices in online shop ( for example YesAsia ) ?

I just want to make sure I won't be scammed >.<

Thanks!