Check blocked users
If you want to know which users are on your blacklist, make a GET to the API with your cust_id in the URL:
curl -X GET -H 'Authorization: Bearer $ACCESS_TOKEN' https://api.mercadolibre.com/users/$CUST_ID/order_blacklist
Remove blocked users
If you don’t want to block a user from making bids anymore, you can remove him/her from your blacklist by making a DELETE to the API with your cust_id and the blocked user’s cust_id.
curl -X DELETE https://api.mercadolibre.com/users/$YOUR_CUST_ID/order_blacklist/$CUST_ID