I have been selling online for a few years now, Ebay was my second platform the first was Amazon but I decided to write about Ebay first for whatever reason. I'm no expert or anything but I do have experience and I have learned a good bit. I have done a great deal of research as well. I have met with success at selling online, nothing amazing but fairly good for part time effort. There are plenty of more successful people out there but I do ok.
So for Ebay, as a seller you have a good bit of control over things. You are supposed to take your own pictures of items you intend to sell, and you should anyway. When it comes to selling stuff on Ebay anything can be the deciding factor. People naturally think that price is the main factor, and for most buyers that is likely the case. However some people will go based off of the idea of free shipping even if the price of the item and shipping is cheaper then the item being sold with free shipping. Some people buy based off of how quickly the item will ship out, a next day handling time can get the attention of some buyers even if it means paying extra.
Going beyond price, if you have a better written description or pictures that are more clear you can get the sale even if you are selling the same item as several other people. I also recommend having items open to receiving offers (that is only for items listed as Buy It Now) if you have Auction items with Buy It Now prices you have to pay for that actually, a listing fee. And for myself my goal is to not pay listing fees. You should also put some research into categories for listing, depending on how people search for things you can be the first thing they see if you get good at selecting the category. That is for a more in depth post then this will be tho this is a sort of overview.
You should have your items a bit higher then you like, that way when people make offers it wont be too painful. You have to try not to get upset at low ball offers because everyone is there looking for the best deal. Another benefit from this practice is when you relist an item that didn't sell you can come down even just slightly on the price and ebay will generate an email to everyone that previously looked at the item that it came down a bit. Now the key here isn't that the price dropped it's that you have an email list effectively of people that are sure to be interested because they looked at it. So you wouldn't want to do a big price reduction necessarily and you can see how many views and item has when you go to relist so when it has a bunch of folks who looked is a good time. It is just another way to generate a bit of interest. Just be careful not to get carried away and discount your item down to where it is not into profit for you when it sells.
Be careful on spelling, you don't want to miss sales because you made a typo. You can look at competition in two ways, see who else has the same or similar items listed and what prices they are looking for or you can search for sold listings of the same or similar items. Most people seem to favor checking sold items, one main reason being searching the current items gives results that can change every day as more sellers upload items. But like I said before it is not always the cheapest option that sells on ebay. People make decisions in odd ways sometimes. having said that if you can afford to list at a price competitive with other sellers it is a check in favor to your chances.
If there is anything people would like to see specifically let me know. I plan to write a little something about sourcing items at some point already but if there is any other factor of it you'd like to know let me know.