D7: How can I list duplicate entities based on the entity title and bundle, without custom coding There is a module for removing duplicate nodes, but how to delete duplicate entities (in my case ECK entities) based on title and bundle that are the same?

I was thinking that the search api module might be of help, which I installed. But listing duplicates requires something extra.

I also have Rules installed, but not sure how to create such rule.

What would be a recommended way to do this?
I'd look at the Entity Bulk Delete module. This module provides a Drush command that can bulk delete arbitrarily specified entity types. 

The caveat here is the module does not delete based on your specified logic of duplicate titles. For that, you can modify its EntityFieldQuery in the _entity_bulk_delete_query() function so it matches your criteria for deletion removal.