on ebay always watch the customer feedback... if they sell a lot and have close to 100% satisfaction you can be pretty confident that what you are buying is authentic. as with anything, don't just bid on the first thing you see that you like, shop around. i buy on ebay often and if you come back a few days in a row with something in mind that you want you can usually come away with a great deal. i learned not to bid on the first thing i saw that i wanted cuz id always see it soon after for cheaper.
ebay is a great source for designer clothing like armani, diesel, von dutch, banana republic, versace, gucci, energie, cerruti, zegna, prada, dolce and gabbana, you name it. designer clothing is the way to go now days for a great classy style.
as a few people said before you classier your dress the more it gets the women wet. sure you may like the baggy pants and gansta look but it just doesn't do the trick like more fitting upscale clothing. the idea is to look successful and symetric while maintaining a good taste and color selection. women really notice shoes also.