I think I've heard of this trick. What the developers do is that they make the app expensive ($500), then they purchase it with promo-codes, leading to it going into the top-grossing list. Then they switch it to 99cents, but since it takes some time for it to slide off the top-grossing list, a lot of people buy the app. This gives it enough sales to break into the top 100 of the category charts, and it will then use that momentum to rise up.

Devs use such tricks - if you keep in touch with the forum, you'll see some crazy stuff people are doing to sell.