You are able to specify a field for product sorting, but not a secondar field. This has been mentioned/requested a number of times by our customers who would like to choose a second field to aid the sorting of products.
For example, they may select an Item Attribute (eg. Product Type) as the sort field, but then there is no additional sorting within that. Currently it seems as though the items are returned in a random order, or in some cases, Item No. descending which is just strange.
If the customer could set a primary sort field, then a secondary one (if necessary), this would be great.