One way to make money on eBay that a lot of sellers underestimate is by making money on returns. Items get returned to almost every seller eventually as its impossible to satisfy all of the buyers all of the time. By turning your returns into profits you can make money on eBay without simply selling your items.
If you are going to make money on eBay from your returns then it is important not to refund shipping charges. You will probably make money on eBay from your shipping charges anyway if you are using cheaper materials and have a standard shipping cost for items, regardless of their weight. If you just refund the charge of the returned items but not the shipping then you are going to make money on eBay because you will be able to charge the same shipping cost to another buyer who bids on the returned item when you relist it. As you have already made a profit from the shipping charge the first time, you are going to double that profit the second time you ship the item and be able to make money on eBay from your returns that from your original listing.
To help you make even more money on your returned items you can charge a restocking fee. This is not something that buyers particularly like and it may lead to negative feedback but you are within your rights to charge a restocking fee and it is a surefire way to make money on eBay from your returns. It would be advisable to only charge a restocking fee on more expensive or bulky items to lessen the chance of receiving bad feedback which will have a negative impact on your chances to make money from eBay by reducing your sales.
If you have an item returned then the best way to make money on eBay is, of course, to list it in another auction. However, it is important to take note of the reason for the return to ensure that it does not happen the second time and make it impossible for you to make money on eBay from selling the item as it keeps getting returned. If the item was returned because it was not what the buyer expected then you have to make sure that you write your description more clearly the second time around to maximise your chances of having a satisfied buyer and being able to make money on eBay that you intended to in the first place.