Where you decide to sell on line can make a huge difference whether you make money or not. Some selling venues are much bigger than others and get more profit. If those sites charge you so much in fees, especially listing fees, you might end up working a long time before you receive any profit. I doubt anyone wants to learn the ins and outs of selling on-line only to pay out any funds received and walk away with nothing. Thus, it is VERY important that you research what type of venue might be the best for what you want to sell.
I strongly suggest that before signing up with any venue that you take the time to really study each one thoroughly. Read ALL the rules as you don't want to be suspended right out of the gate for trying to sell something that you shouldn't be. Just because one site allows a product, doesn't mean all sites permit it. Prior to signing up for eCRATER, I spent two weeks, reading their rules, reading their FAQ (Frequently Asked Questions), and reading the forums that they have. On the forums, are pretty much all the other sellers grumpy and complaining or do they have a positive mindset? This can tell you a lot about a site. Are you seeing a lot of complaints about slow sales? See what the others are saying is the cause and try to figure out if those with the reasons for slow sales are correct. For those that are reporting good sales, they are the sellers that you want to go to their sites to see what they are doing differently than the other sellers. How come they are selling when nobody else apparently is?
Why is it so important to spend so much time in research? So you know what you are doing when you sign up and start your initial listing. Don't be the newbie I saw once that after signing up on eCRATER asked, "Who provided the product to sell and who did the shipping?" I may repeat this example frequently in this blog as that is the most extreme example of someone without a clue. Many others I have seen over the years come on board to sites and then ask questions that they should have known about before signing up such as fees. A selling venues fees can make or break a seller if they don't account for them in their pricing and if there are listing fees (fees charged on a monthly basis just to have items listed for sale on the site whether they sell or not) on top of FVF (Final Value Fees - usually based on a percentage of the selling price). When you add those to the fees from the payment processors like PayPal and fees charged by e/postage sites such as Endicia or PayPal, you may be paying out much more than you bargained for. So be sure in your research that you know the fees. You also want to know what you get for those fees.
When you start sorting through the different on-line venues, note what each one emphasizes as important to a seller, such as how many photos are allowed. When I was looking for a new venue, I was impressed with eCRATER allowing 10 free photos compared to where I had been where only one photo was free and if you wanted more you had to pay more which is yet another way to nickel and dime you to death. One very big help in deciding where you might want to start researching first is on ecommercebytes, an on-line newsletter that reports daily what is going on in the world of on-line selling. One of the things that they do each year is a survey of sellers for the best venues. You can see the results of 2014's survey here. This is not an exclusive list of selling venues, but the top venues that are being used. If a site that you have found seems interesting and just right for you, don't despair that it isn't a good site; it just might not have gotten a head of steam yet to blow the other sites off the tracks. What is important is that you choose a site that you are comfortable with and seems to have what you need for the product that you have chosen to sell.
For some reason this year included Pinterest and Facebook as selling sites. I know that somehow Facebook can have a merchant component which I could never figure out, but I know for sure as a heavy Pinterest user, that you can't technically buy or sell there. You can only present your goods there and hope that buyers will click through to your store. I have had sales directly attributed to Pinterest so I urge sellers to use it. Facebook is another story for me as I find it gets clunky to use so except for keeping track of friends and family I don't do much with it. That doesn't mean you shouldn't. I live with a chronic health problem that saps my energy and I can only do so much. But if you have the time and energy, go for promoting your goods on all social media that you can find.