Ratio of sale transactions to the mid-point (between the minimum and maximum number) of the impression range. Note that the number of items sold can exceed the number of transactions (sales) if a single sale has an item quantity greater than one. An "impression" is any time a buyer sees a search results page that includes the listing. Impression counts can be greater than unique item views.
Note that salesPerImpression impacts Best Match results for only Fixed Price items.
See the Field Index to learn which calls use salesPerImpression.
Ratio of unique item-views to the mid-point of the impression range. An "impression" is any time a buyer sees a search results page that includes the listing whereas "unique views" counts each user only once.
See the Field Index to learn which calls use viewItemPerImpression.