<i>Do all bought items from a city and you get your names in the credit and will go down in history as a badass (really). Claim your city today!</i>

Cities can be a lot of work, you know. By asking that one person has to do a whole city, instead of just contributing one shop, you're raising the treshold to start contributing. Why not mention in credits everyone who contributed? Contributing a whole city can be major inconvenience, while contributing one or two shopkeepers is not. People aren't likely to take up a large workload to gather your list, but might chip in to help out one shoppie or so. Everyone contributing should be mentioned in credits.