Most people make money on Ebay by selling their old items or things around the house they don't need anymore. Others go to live auctions or garage sales every weekend hoping to find hidden treasure that will fetch a nice price online. Of course the professional sellers have a store or some source where they buy things for wholesale prices and hope to sell them for retail prices on Ebay.
Many of us have another source for our Ebay items. That source is Ebay itself! For years I have checked certain items daily in hopes of finding something listed for too low a price or for "lots" of items that when sold individually will sell for more than as a group. Don't be mistaken, this is hard work and needs perseverance. Not hard work like digging a ditch, but hard in its own way. Lets examine these two ways of turning a profit.
The first is finding items that have a too low "Buy It Now" price. If you are successful in beating others to purchase it then you will be able to turn around and sell it for what it is correctly worth. This takes a lot of knowledge because you have to get a good feel for what certain items are worth. People who are professional auctioneers or are in the antique business might be very good at this.
You can also find items that are misspelled and thus will go for too low an amount since very few people saw the auction. I have had my handful of items over the years that I know inside and out and have been able to successfully buy and sell for sometimes a very nice profit. I would look search for these items on a daily basis hoping to find something misspelled that few others would see.
The second way of making money is to search for groups or "lots" as they are called. In this scenario you may be able to find someone selling a "lot" of one thing that you can break up and sell individually for more. I have, on numerous occasions found someone selling a large lot of CD's or DVD's that are all the same. For example, rather than spend the time to sell their brand new Toby Keith CD of which they have 50 copies in 50 different time consuming auctions, someone may choose to get rid of all 50 at once for a decent price. I, on the other hand, am willing take the time to list them individually and might be able to make a couple of dollars on each one for an overall profit of $100.00.
If you know a niche or item really well you may also be able to find something hidden or overlooked in a group of items. In a similar scenario to the last one, someone might have a collection of DVD's that they no longer need. They might put them up as a group not realizing that one or two of them are collector's items and worth a lot more than the others.
An observant potential buyer may recognize this and be able to make a tidy profit on the deal. This has happened to me as well as I once bought a group of DVD's in amongst which were 5 DVD's that were out of print and I resold for over $50.00 each!