How does this work?

SCAM

Buy and sell on Facebook

This is not a scam. This kind of business has been going around for a long time. You simply buy the products that the seller is trying to promote, submit the order information and write a review if requested by the seller. You will get the refund for the purchase amount and a commission for the review, which you can transfer to your PayPal account. You can also earn commission by clicking helpful on the reviews that other people have posted or by just browsing certain item that the seller is requesting for. If you don't need the items you purchased just sell it on Facebook, OfferUP etc for more earnings.