I think of the gag the improv group Improv Everywhere played on a local NYC band. It was chronicled in a segment on This American Life called "The Best Gig Ever."
They picked a local band, one with no particular following, and studied their music. Learned the lyrics, the band members' names, etc. Then one night as the band stepped out on stage for their typical no-crowd, late-night gig, IE was out in force. They cheered, applauded, sang along, called out requests for certain songs, and basically gave the band the best night of their lives.
The band went home thinking they were finally building up some steam. Then the let-down occurred and IE realized how cruel their hoax actually was. No more crowds materialized for the band. There was no momentum. They had been set up, and then came the fall.
If I got a sudden uptick in sales, I'd be thinking about that hoax. Maybe IE or some other group has gotten together and said, "Hey, let's all buy Jan's book! Tell everybody you know!" Sales go up, but of course, everyone returns the books after seven days.
Could happen.