I've been trying to sell Pokemon cards basically anywhere I can, Ebay, Mercari, Facebook Marketplace, and TCGPlayer.
So far I've liked TCGPlayer the very least because I feel like the prices are that site are horrible and the shipping is terrible and the fees make it impossible to get anything back on your cards.
Ebay and Mercari have been the best performers so far with Mercari coming out in terms of experience and return.
Ebay has the larger user base I feel like though.
I'm trying to take advantage of the number of free monthly listings that I get on Ebay. I've logged almost 200 listings so far this month but it's mostly with bulk cards so far.
I've sold some of the nicer cards on Mercari but will transfer them over to Ebay too for whatever doesn't sell.
Very good information that you have given to me personally helps me a lot to do things better from now on on those platforms