HI 

I am in the same boat as you and have had close to 10 customers email me in the past 2 weeks complaining that their item has not arrived... and I post within 24hour of the buyer paying...

Most of my items are sent as large letters so there is no tracking and it is not worth adding tracking to the item because it would kill the profit... I explain to all the customers it is not my fault and it is on Aust Post , after I send out items it is out of my control. most are happy but some still do not get it...

I just saw on another threat that I can buy Priority stickers for letters for an extra 0.50cent per letter... I will be doing this now for the items that have a little bit more profit in them or for customers that are in WA for example... 

I also ordered a date stamp which I will be using to stamp the date on all my bubble mailers so the customer can see the date that their item was shipped.

Not sure what else to do other than stop selling lol