From Apple's Japanese Dictionary:
〔大道商人の〕a decoy, a plant，｟米俗｠ a shill; 〔劇場の〕a claqueur，｟集合的に｠ a claque; 〔競売の〕a by-bidder
さくらを使う｜employ a decoy
The history of this use is also interesting. I first heard of the term at a meeting in November. We were discussing a lecture to be given by the chief of the Mazda motor company at Hiroshima University. One professor mentioned sakura
and I observed that November was not the time of year for cherry-blossom viewing. Everyone laughed and someone explained what sakura
were. The questions were planned beforehand by graduate students, who would earnestly praise the speaker's performance and then ask an innocuous question designed to allow the speaker to shine even more brightly.
In the big Kokugo Dai Jiten
, the meaning is given as a derivation from cherry-blossom viewing, which are large gatherings of people doing something for free. From there the sense became people being planted to pretend to be spectators at a public spectacle, like a theater show or stalls at a festival, and loudly praise what was on offer, in order that people would pay to see the spectacle, or buy goods from the stalls.
So, while not planted, my review essay is plausibly a sakura
, designed to encourage people top buy Ellis's book. Except that I haven't been paid to praise it.