An advantage of having a domain name is you can direct potential buyers from anywhere on the net because search engines will eventually add your name to their databases.
The actual domain name should reflect your wares and so also attract attention.
However your items for sale will be on eBay and people can then arrive via an internet search to your Auctiva shop which looks all professional. They can then peruse your stock as though you had an eBay gallery picture attached to each of your listings. (To see pictures in your eBay shop list would require a gallery picture which requires a fee).
Whether you use Auctiva's or eBay's checkout etc depends on personal preference, at present I use eBay's as it seems a lot of the extras from Auctiva are to do with postage and insurance which are not suitable/available for UK based sellers.
Directed through Auctiva or not, well if the listings are being created on Auctiva why not ?
Remember what I said about quality of the listings, so many seem to get hung up on having flashy shop fronts.
