https://www.comc.com/Promotions/Port_Sale
These are sales of groups of cards from 100-5000 at a time for a single price. All cards are already listed for sale by one person, and you can browse through all of them and make offers for the whole kit and kaboodle. Then if they accept, they all get loaded to your inventory and you can choose to reprice them or have some delivered to you.
Some ports (portfolios) are worthwhile, some are highly overpriced looking for a sucker.