It's difficult and usually becomes more about managing business finance than the products in my opinion. It seems like this type of business is mostly covered in Entrepreneur magazine, or Inc, but they're always feel good success stories.

I helped build a fairly successful online business that sold a single laptop accessory which we had produced, packaged by hand, and sold directly to consumers. The site generated 60k in yearly revenue on somewhere between 5-10k (Christmas peaked at 20k+) unique visitors per month. The margins were really good since we had it produced ourselves and priced high. It was great business while it lasted but I ended up walking away from it because of partner issues.

My old partner still operates it today and it's nearly 4 years later! She tells me that it still generates about half of what it did at peak, but it's slowly fading away because of bigger companies that deliver a better, and cheaper product.

It's great experience and takes time but isn't hard to do.