Not to mention if this was your plan, you would need to add a premium on the price tag for shipping - plus you would be responsible for any damages that occur during shipping. For reference, shipping a Full ATX tower + 24" Monitor will cost you around $200 with UPS depending on where you're shipping to.
Also keep in mind that if you do create a website and attempt to make a full business out of this, you'll need to know search engine optimization or use Google Adword to get your website to even show up on the first page of Google results, and let's be honest - few people click page two, and only the truly desperate ever navigate the barren wasteland that is page 3+.
As was mentioned before, you would need to be viewed as more trustworthy than say, the other 20+ manufacturers.
To finish, if you're just looking for money on the side, I would advise that you do what several acquaintances of mine have done in similar situations.
Go to various websites, such as Craig's List and purchase broken electronics and computers for dirt cheap. Figure out what's wrong with them, fix them and then sell them for a large price gain. If you're planning to make a career out of it, you'll need to start small. Make sure you practice what you're doing, and then try to get a job at a local repair shop while studying how to go about creative a small business on the side.
Hopefully I was able to help you with this answer, but if you're dead set on your original plan, there's many website builders that can help you along the way.