While TCGPlayer does have a pretty large user base and it has some extremely competitive prices and useful tools for both buyers and sellers, I am finding it extremely difficult to manage my inventory when I'm also selling on Ebay, Mercari and occassionally Facebook marketplace as well.
TCGplayer does not provide it's sellers with any kind of bulk or easy to use tools for their sellers from levels 1-3. Everything is SUPER SUPER manual and takes forever to manage.
I haven't made it to level 4 yet but hopefully it gets better from there. I've decided to pull down my entire inventory for the time being though until I can manage to to work up the strength to keep going on here.
For now I much prefer Mercari and Ebay.