Working on Project for School, Need Direction..

Hello everyone, I'm working on a project for school and was hoping to get a little direction from someone.

Basically we were given a business idea and we need to explain why it is or isn't a good idea. The idea that I was given was an idea for a website where items are pulled from numerous online retailers for side by side comparison and shopping (Like Wal-Mart, Amazon, Ikea, random local retailers). Where I'm looking for guidance is I'm not exactly sure where to find the legalities of such a venture. Would these retailers allow another company to list their goods? (doubt it). Will I need to investigate each of them to find their policies on such situations? Also what laws prohibit it (I'm assuming some sort of property violation)?

Thanks for the help in advance, I figured this would be a good place to find some answers.