You are actually looking to lunch a small business? You have something to sell?
Probably the first idea to show up is when you see how individuals can buy effectively on eBay. And that may be true, and you're trying to compare that to yourself and saying: I CAN DO THE SAME.
eBay is great, you can in a second open an account, put your product and wait for bidders of fix your own price. Sure that there is some points that I'm ignoring that can increase your chances to sell as confirming your account, putting well taken pictures, and provide a complete description.
You may ask why than thinking about create a website, and so a web store from scratch?
So I would reply to this with the following points:
1. Kind of product
If you are providing unique products or selling your own used stuff, or those you bought and didn't use, than for sure I would recommend eBay. Also you can consider it if you are producing something and you don't have enough budget to go for your own.
2. Your vision
If you are looking to sell something to get some benefits, or, you want to do a real business that can grow? This will change your decision for sure. When you create your own site, you are creating your own brand, and if you know how to market, people will buy from you as a business not as an individual. And also they are expecting business interacting and not one-to-one.
3. Your budget
This may be the point that can force your decision, because when eBay lunch is for free. Creating your own site should cost you much, starting for $500.00 up to much more. While you have to pay for the development of the site, the hosting, the domain name, and you need to think about PayPal or your local bank to receive the payment.
4. Competition
If you are selling conventional product, may be phone accessories, that would be very hard to sell on eBay because of the rude competition. Every one can provide the same product with very competitive prices. Which will not allow you get a good profit. Unless you believe your prices are very good, or you're providing special features as free shipping or worldwide shipping.
Those point at the major differences that you can face. So think wisely before making the move.
You should may in the case you have a limited budget and your vision is you go for a real business, than you can consider taking that into separate steps. Start selling you products on eBay while building a simple website. If you are not including selling features to that it will be cheep to build. Or consider social media to promote your brand as this is a free way to do.
As you may see, it's very easy to start a business, but because of the numerous options that you have, it's not easy to decide where to go and how to start. So I hope that this will give you a better insight.