Fake counters are commonplace on countless eCommerce stores, and Booster Theme has a few of its own, including the visitor counter. Basically, it shows a fake number of visitors that are currently using the site and looking at the same product as the real user.
The idea behind this is to make products seem very popular to encourage users to buy them. The effectiveness of this strategy varies, as some buyers prefer products that aren’t widely available (think a unique t-shirt design), while some are encouraged by its perceived popularity.
You can easily turn this off, so it may be a case of trial and error to see what works.