I did a subject search on an agency for one of my biggest-selling images recently - using their 'Most Popular' algorithm.  I have two variations on this image, and found that the one that sells the fewer of the two was way up in the first couple of rows of page one in the search results.  Meanwhile, the higher-selling one that FAR outsells it was not even listed for several pages.

I presume that means that 'Most Popular' weighs views against purchases, and that the lower-selling one has had more 'views' result in purchases, while the (vastly) higher-selling one has had more views that did not result in purchases.

Do I have that right?

Oh, thank you Gostwyck, good thinking!  That did not occur to me.  I will check.