Carpets? Even if you dont need one, it'll be really hard to leave Kairouan without one. It's the carpets' capital - and everyone will try to sell you one. If you are weak, you'll most likely come home with one: in this case make sure at least it's hand-made. How to do this? Easily? Turn it backwards: if the design is the same as the design on the front, then it's handmade.
When you walk through the souk it'll be easy enough to say no - or in the worst case just to keep on walking and ignoring the yelling salesperson. The real problem starts when you enter a carpet shop - especially when you are cheated into one. Touts will stand outside and tell you to go inside: it's a Mosque, the Governor's house, someone famous house and that the architecturee is wonderful (it's true btw)... Once you enter you'll see that yes, that USED TO BE what they told you but now... roll of drums... it's a carpet shop. We fell in the trap and got stuck in there for over an hour - they simply would not let us leave - we only managed to escape because I was offered a "precious" carpet at a very convenient (still expensive) price. I spotted it as a machine-made one, an heated argument followed (I just pretended to be really offended to be cheated just to get to the exit door) and finally declared I would not buy from a dishonest man. Only then we are allowed to leave.