If you didn't know already, you can buy your way up to the top of the App Store. I myself am not technically sure how it works, but you can pay a company to create false installs of your app, driving it up the rankings. If you spend enough, you can get your way into the top 10 - where every app developer wants their app to be. TradeMob has come up with a informative infographic showing the costs and how it all works.
The App Store is based on regions/countries and of course the US is the biggest market, followed by the UK. By getting your app into the top 10 you'll then be able to acquire organic installs which could make up for the money you spent. The US App Store requires around 80,000 installs in the last 24 hours to get into the top 10. To acquire 80,000 installs it'll cost you around £61,500. The organic purchases would then kick in which could make up for the money you spent. But of course if your app is a pile of shit, it'll go straight down again, helping you burn £61k in the process.