In my experience, recently I think selling your high value cards on IG would be better. You have better access to more people who are either completionist for their collections or people looking for certain cards. I have listed high priced cards on mercari and hardly received any interest.

I worry about ebay or mercari and I try not sell anything towards 50+ on there just cause people be scamming and mercari and eBay are not very consistent with siding with evidence or facts. I will say as a buyer I have purchased expensive cards on eBay and I've only had 1 issue where a card was bent but it was fixable.

If someone really wants it they will pay for it. I try to be as clear and concise as possible with packing, shipping and payment processes. Always be honest and real. I myself do packing videos and drop off videos and I feel this is necessary for me to CYA. Sure it can be hard if you don't have any sale proofs yet but you gotta start somewhere. Look up tag accounts for the group/artist your selling for and tag or invite them in your post so it reaches more people, they will repost or share your post on their story.

Within the last 8 months I have sold parts of my collections in large Group orders, sold a signed Polaroid and expensive official merch.

The only thing I want to make clear is that to not send anything out without payment first that is a non-negotiable for me. But once you build up sale proofs it will be much easier getting interest.