It appears that 400 x 400 seems the norm.
Would I pre-edit my photos to this size before adding to item ?
Would any other size ( say 600 H x 400 W ) be cut to fit ( missing heads ) or reduced to fit inside the 400 x 400 ?

PIXCONVERTER seems a good little solution.

Question
I will be starting with Nikon originals of over 1 megabyte.
Can I simply opt for 50% quality, select a custom 400 x 400 and tick the 'maintain original image proportions' ??

The software will automatically re-size them for you. If you would like to re-size them before you add them to Shopping Cart, the optimal dimensions would be 90x90px for the thumbnails and 400x400 for the large image.

Downloaded and played with Pixconvertor but even at 20% quality the images won't go below around 900k ( irrespective of original image file size, around 1.6 meg ).
I tried Web and Auction.
I tried 50%, 30% then 20% and final file size still around 900k and won't shrink...lol
These are still way too big for uploading ( quickly ).

BTW Scott. Thanks for taking time during your break.