Hiring new characters is free. New characters start with a weapon. You can sell these weapons. The warrior one sells for 2 gold, the wizard and priest ones for 1 gold. If charslots are infinite, you can abuse this infinitely. As a sidenote: I can't find any way to delete a character permanently, so you can get quite cluttered up.
Already reported - and devs were hoping you'd not find it until they could sort it out. http://www.cardhunter.com/forum/threads/inventory-management-bug-possible-lame-exploit.450/
Oh well, I found it by accident when I was recruiting to make different party setups(as well as do the all-class, all-race quests).
