Most of the items you see selling on ebay for less than what you can buy them from a 'wholesaler' are because of several different things..
First, most wholesalers who sell to you, also sell their goods on ebay. Naturally they can sell their own stock cheaper than you can..
Secondly, there are a ton of people out there who claim to be 'wholesalers', selling you goods at 'wholesale' prices, who are really just 'middlemen' who are in fact, just really buying their goods from a 'true wholesaler' and then marking up the goods and selling them to you at a price they claim to be wholesale, but in fact really is not..
Thirdly, some of the larger sellers buy their goods in very large quantities and therefore are getting 'bulk prices' which enable them to sell at a very cheap price. They make their profit buy selling large amounts of goods and only profiting a small amount of each item, but due to the large amount of items, enables them to make a nice overall profit...
There are several thing that you can do.
First you too can buy in bulk and sell at a reduced price to beat your competition..
Next, you can try buying 'liquidated' and 'surplus' goods. You can get liquidated and surplus/closeout goods at litterily pennies on the dollar..This will enable you to undercut your competitions prices and yet still mark the item up enough to make a nice profit..
In addition, and I've said this many times, don't always try to sell what everyone else is selling. Take a look at common 'everyday items'. Things that people use and need everyday. Common household items and things like that..These types of items are easily aquired and normally can be found at local thrift and dollar stores at very cheap prices...
Most people get hung up on thinking that they should be selling all of the 'designer goods', fancy electronics and things of this nature, and are unable to find these types of products at a price to be competitive..There is simply too much competition and too small of a profit margin to survive selling these types of items.
Think 'outside of the box'. Remember, not everyone lives close to a shopping center, or works normal hours. These people normally shop online and they can easily become your customer, since they are normally overlooked as a potential customers...As I've said before, one of my daughers makes several thousand dollars per month selling coffee mug and kitchen decorations. Gets them at the local dollar stores for about a dollar apeice and sells them on ebay for 10-15 dollars a set. That's an example of an everyday item that most sellers simply overlook, because they think no one will be interested...
Think about things that you might want and need, but don't really have the time to run into town to get...These types of things will be wanted and needed by others people as well...
One of my biggest sellers was a brand name cosmetic makeup line, that only sold through it's own boutiques. I use to buy the stuff at the boutique for retail price and resold it on ebay at a very large markup...All of my customers were people who liked the makeup, but did not have a boutique in their town, so they happily bought from me....
So don't get discouraged. It just takes some homework, research, and a bit of trial and error, but if you stick with it, you can and will make money....