One neutral won't hurt you, don't give up yet.

Maybe, when you send an item in future include a pre printed note/card :

Thank you for purchasing "blah blah" from "blah blah" -  if, in the unlikely event you are less than 100% satisfied with this item, please do not hesitate to contact me on xxxxxxxx.com.au or 1234567 so I can work towards an amicable solution for any problem you may have.

I sent the same message (roughly) on an invoice whenever I sent an item, and so far, has  not failed me.