Category_in return empty

You can achieve that using the tax_query, see the example in the code below:

$args = array(
  'posts_per_page' => 10,
  'post_type' => 'product',
  'post_status' => 'publish',
  'tax_query' => array(
     'taxonomy' => 'the_taxonomy_slug', //the slug of the taxonomy you want to get
     'field' => 'term_id',
     'terms' => $categories
  ) 
);

See reference in the Codex