I have to start by saying that I'm not currently involved in online sales through any platform, but have been in the past (very successfully) and will be again very soon.
So while I can't really give you specific examples, I can give you some general answers.
To your first question, is online sales your main source of income? There is no reason why you can't make it your main source of income if that's what you want and you have the ability to do it, but something like that isn't just going to fall into your lap, it depends on so many factors.
For example, with me going back into online sales again very soon, it will be my main income source or I should say that I am going to be working hard to make it that over time. Now for me to do that, I am going into the market with a fully independent website and a unique range of products, not relying an Amazon or eBay as my primary retail avenues, although I will be using eBay as a marketing funnel.
I know my products inside out and I know my market extremely well, both primary and secondary. Because of that, I also have developed, what I believe, will be an effective marketing strategy that will enable me to hit my market on a worldwide scale for the best possible value and give myself the best possible opportunity of driving traffic to my site and converting a lot of that traffic into sales.
Just as a foot note to that, I've also had these products custom designed for me and I've completed a full scale business plan as well.
Now I've just given you a very quick outline of the effort I am going to in trying to make this a success and I have done that to give you a bit of an idea of the difference between a serious full scale assault on an online retail model and something like a drop-ship model selling on Amazon.
They are absolutely poles apart!
So yes, it can be done, but it's not a walk in the park.
If drop-shipping on Amazon is going to be your main driver, then the chances of you ever making that into anything more that just a part time income stream are extremely difficult.It can be a good starting point for people, but to turn that model into a full scale online retail success is going to take a lot of development over time.
There is a marketing term called POD (Point Of Difference) or also referred to often as USP (Unique Selling Point) It's about defining yourself in your market space, what is going to set you out above your competitors to encourage customers to by from you.
Think of drop-shipping on a multi seller platform such as Amazon like this. A massive shopping mall where you live, 1000 shops in total inside this massive mall and all 1000 shops are selling pretty much the identical things to each other. Now that sounds bizarre of course, who on earth would set up a shopping mall like that, but that in essence is what Amazon is.
Now if you were setting up one of those 1000 stores in that shopping mall and you were shop 499, pretty much right in the middle of the mall, a very big question you would need to be asking yourself is "what can I do to create a POD to ensure customers walk past 498 other stores and buy the products from me?"
That's a question that everyone using a multi seller platform like an Amazon or an eBay to drop-ship products need to ask themselves, especially popular products that have a very high level of competition.
That in my opinion is one of the absolute keys to success, developing an effective POD!
It's not just a simple matter of building it and customers will flood in. Now there are plenty of people will tell you that is all it takes or they have some secret to your ultimate success that they are happy to share for a small nominal fee, but that's just plain garbage.
There are no secrets to online retail success, but there are keys to success. This is a business and as with most business's, if not all, the more effort you put in, the more rewards you stand to get out out of it. The one thing you can't do is let yourself get discouraged, that will just eat away at you until you end up giving up.
Start with a clear head, id your objective and develop a well flushed out detailed business plan.
That's where all successful buisness's start, with a well thought out business plan. It's road map that clearly identifies where you are currently, where you want to get to and how you can get there. If you really want good long term success in online retail, I don't think there is any other way to do it personally.