1. Getting involved with products you don't use yourself. Falling for the DROP SHIP system.
2. Thinking you can buy SEO results. That's money badly spent. Folks that sell SEO will be quick to disagree. Simple thoughts on that. Who's getting your money?
3. Expecting a return in weeks not years.
4. Building a custom web page. I have stories about companies that did this, lost 6 figures USD and were years late getting their commerce site working. If you want to start now, start now. GoDaddy, Amazon, hit the ground running.
What is the biggest mistake you can make when deciding to start your own business?