Online Marketplaces:

Ebay – Ebay is likely the largest online marketplace for selling individual baseball cards. The buyer base is massive which gives you the best chance of finding interested buyers. Listing cards on Ebay is free, though you’ll need to pay a final value fee which is usually around 12% of the final sale price. One downside is that fees can eat into your profits. The sheer size of the user base makes it very likely cards will sell. When listing, be sure to include clear, high resolution photos of the front and back of each card along with a detailed description listing any flaws or issues. You’ll want to price competitively after researching recently sold listings of similar cards.

COMC (Cardboard Connection) – COMC is a site specifically focused on trading cards. They do the photography, description and customer service for you so all you need to do is send your cards into them. In exchange they take a larger percentage (around 20%) than Ebay but you don’t have to list or ship individually. They have a large userbase of collectors actively buying and selling on the site. One potential downside is there is less visibility for individual cards compared to listing them yourself on Ebay. Still, for bulk Lots or large collections it can be very convenient.

Sports Card Direct – Another site focused primarily on sports cards including baseball. They do take larger commission rates than Ebay (around 20%) but handle the photography, listing, grading verification if submitted for grading and shipping for you. Can be great for large collections you want to liquidate quickly without hassle of individual listing and sales. Customer service is generally good. Again potential downside is less visibility than listing on Ebay yourself.

ComicConnect – While less focused than the above sites, ComicConnect is a respected marketplace for collectibles including trading cards. Fees are generally under 20% which is competitive. Quality consignment services available as well if you want them to handle everything. Again potential downside of less visibility versus Ebay. Best suited for higher end, rare cards that serious collectors will be watching.

Peer to Peer Sites:

Reddit Sports Card Trading Groups – There are active trading groups on Reddit focused specifically on sports card, baseball card trading where users can post cards they have for sale/trade. No fees but smaller pool of potential buyers. Good initial way to gauge interest and value before listing elsewhere.

Sports Card Forums/Trading Sites – Sites like BlowoutCards.com forums have active classified sections for buying/selling. Again no fees but smaller pools. Some forums like SportsCardForum.com integrate well with marketplace sides so you can list cards for sale both places.

Local Card Shops – Most areas will have local collectibles shops that buy/sell cards. You’ll likely get a quicker sale going this route versus online but they will offer you less money per card than a private sale since they need to resell for a profit. Ask what percentage or dollar amount they take per card. Some now have online shops too integrating local inventory.

Grading/Authentication Companies:

PSA/BGS – For rare, valuable vintage cards it is generally recommended to have them professionally graded and authenticated by a company like PSA or BGS. This adds validity and ensures buyers they are genuine. Cards will hold long term value better and appeal to serious collectors. Downside is cost of grading ($10-$30 per card typically). Cards need to be valuable enough to offset grading costs. Both companies have their own marketplace websites where graded cards can be listed and sold through.

Those would be some of the top options for selling baseball cards both online and potentially locally. The best approach will depend on factors like number of cards, their rarity/value, your time constraints and desired profit margins. With some research on recent comp sales and listing your items well with clear photos you should be able to find buyers for both common and high end cards through the various marketplaces. Let me know if any part of this overview needs more clarification or expansion.