Exactly what the title says. What is the best CMS to use? Or should I be purchasing a script? Are these Ebay clone scripts legal?
You're not looking for a CMS. CMS is a content management system and is limited to written content (as well as photos, and membership capabilities). You're looking for an on-line store. There are a number of them out there for free with free templates to start you off: OS Commerce, Zen Cart and CRE Loaded. I am not sure if they support auctions, but you've got a better start with these than something like Wordpress. If anything you can hire a programmer to customize certain functionality for you at a much more affordable price, then trying to code this from scratch. Good luck