Thanks guys.  Skyval, we mostly make corn brooms from broom corn.  They are very durable.  We had a handmade one for 17 years, but the kids packed it of & it got wet.  That broom was made with natural hemp twine.  We make ours with nylon seine twine, which won't rot.
A friend has the sister to our old broom.  She's had it on her porch now for 20 years.  Another came to our booth and said she has a hand woven broom in good shape that is 30 years old.
If you hang the brooms on a nial, and keep them dry, they last for many years.  At least 10.  Maybe 20-30, depending on how much you sweep!