You will need to ensure that you adhere to a few principles when doing this. You need excellent photos, so investing in a good camera is well worth it here. You also need to ensure a meticulous description of the product, new or used. People appreciate the attention to detail and it will go a long way when trying to sell anything through these bustling online hubs.
Next, you’ll want to pick a WordPress theme from somewhere like ThemeForest, Elegant Themes or OptimizePress. This is the barebones design of your site, which you can then customize with your own branding, copy, and images. That being said, you don’t want to cheap out. It costs less than $100 to buy a theme that will make your website look professional (and you can upgrade to a completely custom design once you get the business going).