firstly never ask for feedback, it's pushy and it usually gets you the type you don't want.  Ebay already sends reminder emails to buyers to leave feedback (which personally I hate).  It takes time to get your feedback up, and most buyers couldn't be bothered because it does take a long time.  I leave mine in bulk (when I am buying that is) maybe once a month or something.  Just keep selling and if you don't get negs and low DSR's then count yourself lucky 🙂