I didn't notice it but I don't think it should have a certain impact on vector sales.if a buyer was looking for a vector image I don't think they'd change their mind and buy a photo instead just because they see more photos than vectors???.besides buyers can easily  adjust their search parameters by  the search tab above the page and eliminate the type of files that they don't want to search. I don't know I might be wrong though??

The problem is, that the buyer can not select for/against vectors only Photos and/or Illustrations. My best image that used to be on page 1 for a one word photo search is now on page 7 and is being buried under extremely repetitive illustration renders that are accepted as photos - even though no camera was involved in their creation.

Sux

vectors are useful but lifeless. Most people would search for photos.

The illustrations you are talking about are most likely 3D renders and Photoshop work, which as you mentioned show up under the Photo option even with Illustrations unchecked.  I has been speculated that they show up so high in the best match sort because it may be weighted to show images available in the largest sizes first.

There have been quite a few mentions of this anomaly on iStock's forums.   I believe the best match sort order at iStock is changed or tweaked more frequently than most would imagine. I'm sure with all of the data the programmers have they are always working towards a search that is best for the buyers and has the highest overall sales results.