Here's another way to make easy money. Purchase as many weapons as you can in Bowerstone and Old Town (preferably places you don't own), and sell them to the traders in Fairfax Garden. Your profit margin should be somewhere in the neighborhood of 30% when you do this, but can go as high as 70% if you own the stores. Furthermore, doing this will increase the overall value of your properties! So it's a win-win situation!