MySlabs is a collectibles marketplace, for not only cards, but also comics, memorabilia and toys. Despite the name, you can also purchase both raw cards and sealed wax, not only graded/encapsulated cards.
The differentiation for MySlabs is their fee structure. With a broader marketplace like eBay, you’ll pay more than 10% on any sale – auction or fixed, while MySlabs only charges 2% on slabs and 3% on raw cards, which can save you significant amounts of you move stuff in volume or of a higher value. Sellers are all screened and manually approved to be able to sell on the platform, so you can be a little more certain in your dealings there.
Unfortunately, if you’re outside of the United States, this platform is a little more difficult to use, unless you have a U.S. shipping address available to you. You’re also limited in which grading companies’ slabs you’re allowed to sell. They currently allow the big 4 (Beckett, PSA, SGC, CGC), plus CBCS for comics.