From what I have read (as I am not a seller any more), ebay is in a sort of partnership with sendle, but you don't actually have to use them. I am pretty sure you can still opt to use eg Australia Post and still print out postage labels and so on.

Sendle, as you know now, doesn't actually do the delivering. It subcontracts out to couriers.

A lot of the time in my area, it works out fine but I can tell you this much, if you do strike a problem (as seller or buyer), it is a virtual nightmare to solve as they give you scripted answers over the phone and you're not dealing directly wwith the company that delivered it.

But as rocket2retro pointed out, no matter who you use, the problem with breakages is very real.

I have in the past had deliveries of glassware that was packed professionally. It was already boxed and glasses individually cocooned then the whole packed into a second, solid box. But still, some glassware cracked.

Even if couriers don't actually toss things around, I think it is still possible for things to crack. I'd say you will just need to factor this into your selling prices as if you sell breakables, occasionally you are going to have to refund.