First Twitter, then Yelp and now FourSquare is attempting to monetize their platform. As of today, for a minimum of $50 a month you can now place ads on FourSquare. The minimum bid to reach a visitor is $1.00. That means with a $50 budget you will reach 50 people a month. Here’s the catch… you will only be charged if the person who saw your ad actually checks in! Brilliant!