most ebay companies use cheap materials.
For the most part, the ebay exhausts will not hold up over time, because they are cheap stainless steel, whearas name brand companies use good stainless steel which will hold up to the elements.
Also, the welds on ebay exhausts may break due to poor quality. whearas skunk2 etc will have nice machine tig welds
Ebay exhausts may not fit like a name brand
Finally name brand exhausts tend to use larger piping like 2.5" instead of 2.25"
Although, I had an obx exhaust on my prelude and loved it. It was 170 dollars shipped!!!!!!! it was fully stainless, 2.5" and fit great and held up great for over a year until i sold the car. It sounded WAYYYYYYYYYYYYY better than my megan racing exhaust. I would reccomend OBX if you are on a tight budget, their exhausts actually arent too bad. and you can buy 3 or 4 of them for the price of one skunk2/hks/greddy