I have bought items sold by both AMZN and third party sellers,whoever offers a cheaper price ,reasonable shipping time,I will buy from that seller.
what is the item you want to sell on AMZN marketplace?
(books,consumer electronics,office supplies)
Have done it, and you can generate some sales. But, if you do not use a repricer (not AZ's) then it is useless. When you go below by 1 cent, then AZ matches, and so on. To due it manually is a waste of time.
Also, if you can "see" how low AZ goes with their price (Keepa), then you can see if it is worth it.
But do not expect to make much more than a couple of dollars on each sale, if that.