If we wanted to allow members to list products for sale similarly to Amazon and take a transaction fee, would that be possible with Carthrob?
Cartthrob is flexible enough to allow you to create custom plugins that add functionality - you might need this to automate any kind of transaction fee collection and for reporting purposes (assuming your sellers would want to be able to view reports - this might also be possible via front end templates).
But Cartthrob is really just the shopping cart and checkout bit of the site with some back-end reporting tools thrown in. What you're describing is more basic EE functionality with Cartthrob bolted on to handle the transactions bit for customers.
You could build a seller control panel sitting alongside the public facing site on the front end using EE and use regular templates to pull information for each sellers reports from EE and Cartthrob's data.