I echo what has been said already regarding this issue. When I worked at eBay, I managed the accounts of 218 of the top 1% of eBay sellers, those who were generating at least $25,000 a month or more in sales on eBay.
Every single one of those 218 sellers purchased their products in large wholesale lots (usually $100,000 worth of products or more at a time), and that enabled them to sell the products at extremely low prices on eBay. The only way to compete against those prices is to buy your products in volume like they do, unfortunately. The more products you buy up front, the cheaper the price per item in most cases.
The good news, however, is that although there are many, many products on eBay in which this is the case, there are just as many if not more products in which this is NOT the case, and in which there is a lot of room for competition. I suggest staying away from the more high-profile categories like designer fragrances (along with electronics, computers, video game systems, cameras, cell phones, designer handbags, etc.) and focusing on less-popular products and categories. Less popular doesn't mean unpopular, after all. Categories with fewer buyers almost always have fewer sellers, too, making it easier for you to compete.