Most of your items appear to have been pick ups, so no relevance to postage there,

The majority of FB received is fine, but those 4 neutrals are probably whats holding you back at the moment, not the ratings but assuming those sellers also left low DSRs as well.

List more items to build up your FB, make sure you communicate when buyers contact you, if you aren`t going to state the postage, this will effect your ratings, if the buyer asks you still have to send the cost, so why not state it on the listing.

Check out Click & Send, their rates for flat rate Australia wide for satchels and Aus Post boxes is the easiest way to add the postage to your listings. and the boxes are so cheap to send especially for heavy items which appear to be relevant to the items you are selling. .