Is it best to start a business on eBay or to build your own site?

Its best to do both.

Offer your items on Ebay. That will give you some experience in pricing and sales.

Put alittle thought into a creative domain name. Lets say your product is a new hummingbird feeder. Search for creative names that are open about hummingbirds. The cost can be from $5 to $20 a YEAR. It can be more but I wouldnt do that (at least not yet). If you need help finding a name that is open then ask a new question here about it.

Create a web site. The cost can be free to $20 a month depending on how much easy automation you get or willingness to learn it yourself. Actually, you can get a high school kid to do a pretty good job for a McDonalds burger but you have to hold them back from piling it full of a thousand eye-catching whiz-bang things.

Use your cheap web site to learn webmaking, advertising tricks, getting into search engines, getting your site linked on other sites, etc.

Add other money options to your site. Add “affilliate” links on the same subject. If you are selling a hummingbird feeder then link to Amazon.com books on hummingbirds, AllPosters posters of hummingbirds, CafePress tshirts with hummingbirds, etc etc. Look into using PayPal to add payment options. Look into allowing Google Ads to use a small piece of your webpage for other peoples ads about hummingbird stuff so you get “click thru” money if people click it to go there.

Grow your site. Do reviews of those things you are affilliate linked to. The hummingbird books for example. Also link to hummingbird articles. Create a dynamic link to news.Google.com on hummingbird so that all new news items pop up. Add a blog. Add a forum. Add a guestbook. Add a gallery where people can upload hummingbird pictures.

ANYWAY Im getting carried away. This is one of my subjects. “Any one can net”. (Any1Can.net). At the start you will sell both by Ebays efforts and your own. As your website gets traffic and starts paying for itself you can gradually drop Ebay. You can move it to a more expensive server with more built-in features. Eventually if you start earning enough and getting so much traffic that you are getting hit hard on bandwidth charges then you can migrate to a server you run yourself (not that hard, I do it).

But here is the important part. YOUR DOMAIN IS PORTABLE. Start it now. Its not that expensive. It can start on a cheapo site and move as it grows. That wont affect how traffic gets to it. Dont spend too much on it yet but get it started. Let it earn its way up.