I've just done some tests and it's sort of weird.  If I try to list table tennis bats then when I get to the price and payment screen I get this option where I have to select auction or buy now https://imgur.com/xcr8niK   When I select Buy Now the options appear to set price and payment etc but the multiple quantity is missing https://imgur.com/bAuJaPH   However, if I try to list a light bulb then I get the old screen where you have all the options, my previous selected payment options are prepopulated and I have the option of increasing the quantity.  https://imgur.com/9LuQbtO

I find it annoying. Sometimes I'll use the sell similar item option rather than relist to clear out the old watchers. 

You might just have to go into the sold auction and there might be a 'sell similar' button. 

Is this a within/between island thing? I know for NZPost a small box is $10.17 within the same island but $17.64 if it's between islands.  

Too many fees. In trade sellers are charged 9.9% or more and not just on the sale item but also shipping. Then ping is an extra 1.95%.  For a non in trade seller a $100 general item will have fees of $7.90. Including ping the fees would be $9.85. For an in trade seller the fee would be $9.90. If the shipping was $17.40 (small/medium box interisland with nzpost) the fee would be $9.90 + $1.74 = $11.64. You'd either need to eat this extra shipping fee or you'd have to up the shipping charge to >$19.   Now if you add ping then the fee is $9.90 + $1.74 + $2.29 = $13.93. So compared to a non in ...

I guess this is what the newish "Make an Offer" function is for so. It's only available via the app though.