It all depends on your buyers.

If they understand that Australia Post is completely snowed under at present and all parcel deliveries are painfully slow then you should be OK.

If your buyers are in denial that COVID is having an impact on delivery times then they will be baying for your blood when ebay tells them that the item is late.....many of them will not give even one days grace before opening a dispute.   And ebay will usually refund them even if the tracking shows the item is still in transit.

Yes you can be.

We have a purchase which we made on the 29th of August, posted on the 31st by the seller.  Processed in Dandenong PC on the 11th, which was past the expected delivery date.

Still sitting there,  we could raise an INR and get refunded,  but we realise there is a world wide pandemic, so happy to go with the flow.   But some other buyers would not be so patient.

If I did raise an INR and get a refund,  then it's up to my good nature to either repay the seller or send them back.   It's one of the risks of using any delivery service be it pandemic or normal times.  Once it's leaves your doorstep, you have no control.   Depending on the item you can claim the insurance which I think is $50 from Auspost.   

They recently delayed an express post letter we sent (not an Ebay thing),  which all they were prepared to do was refund the purchase price of the envelope.  It ended up getting to the recipient 3 months later, I didnt offer to repay Australia Post.