Blocking a few products at a time can be done via the Product listing pages, but what if you need to block hundreds of products at a time?
This is when you would use the Bulk Block Feature.
To get started you need a list of eBayLink / Omnivore SKU's you want to block, If you don't have a list, you can generate it via the Export CSV found here
Filter what products you want to block/ unblock.
Navigate to Products->Bulk Block
Paste the list of SKU's in batches of 300-500 (any more than this can cause a timeout 504 error).
You can test the validity or status of products by clicking Test or Block / Unblock by clicking Apply.
Once completed, make sure you do an upload to the marketplace to ensure the products are blocked/unblocked.
Please note, this will block the product across all marketplaces.