In-game purchases are now very common among players of all ages. What most gamers probably don't realise is that video game companies use behavioural psychology to heavily stimulate their customers before they even decide to make an in-game purchase. Mobile games played on phones and tablets, and in particular 'free-to-play' downloadable games, are currently leading the way in terms of monetisation. But how is it possible that a product that is free to download and play can, in fact, generate...