During recent years, the practice of adding game design to non-game services has gained a relatively large amount of attention. Popular discussion connects gamification to increased user engagement, service profitability, goal commitment and the overall betterment of various behavioral outcomes. However, there is still an absence of a coherent and ample body of empirical evidence that would confirm such expectations. To this end, this paper reports the results of a 2 year (1+1 year – between-group) field experiment in gamifying a service by implementing a game mechanic called ‘badges’. During the experiment a pre-implementation group (N=1410) was monitored for 1 year. After the implementation, the post-implementation (the gamified condition) group (N=1579) was monitored for another full year. Results show that users in the gamified condition were significantly more likely to post trade proposals, carry out transactions, comment on proposals and generally use the service in a more active way.