<?php
function dokan_get_sellers_by_term_id( $term_id = 0 )
{
  global $wpdb;
  if( !$term_id ) {
    $term_id = get_queried_object()->term_id;
  }
  else {
    $term_id = intval( $term_id );
  }
  if( !$term_id )
    return;
  /**
   * Query
   */
  $query = "SELECT user.* FROM `wp_users` user
LEFT JOIN `wp_posts` post ON user.ID = post.post_author AND post.post_type = 'product'
LEFT JOIN `wp_term_relationships` taxr ON taxr.object_id = post.ID
LEFT JOIN `wp_term_taxonomy` tax ON taxr.term_taxonomy_id = tax.term_taxonomy_id
WHERE post.post_status = 'publish' AND tax.taxonomy = 'product_cat' AND tax.term_id = %d
GROUP BY user.user_login";
  // prepare
  $query = $wpdb->prepare( $query, $term_id );
  // get
  if( $result = $wpdb->get_results( $query ) ) {
    return $result;
  }
  return;
}
?>