Hi
I would like to show best seller based on user ID. How do I archive this using code ?

In functions.php find this:
function eps_get_users($type = '', $limit = 12) {
  if($type == 'by_items') {
    $order_col = 'i_items';
    $order_type = 'DESC';
  } else if ($type == 'by_reg_date') {
    $order_col = 'dt_reg_date';
    $order_type = 'DESC';
  }
you probably want to change i_items to pk_i_id

Works ,
however I would like to enter user id manual for specific IDs
Something like this $user_id={'1,2,3}

How do I archive that?

add there where statement in way:
...->where('fk_i_user_id in (1,2,3,4)');