What are we looking for in a guarantor?

Guarantor

I am increasingly promoting my houses to housing benefit tenants with guarantors. So far my experience of guarantors has been good. But I am wondering how strict to be in who I take a guarantee from.
I say property owner only but I wonder whether decent stable job is more important?
I say most be near enough to meet me face to face and sign deed with id. Has anyone made them go to a distant solicitor?
I do not credit check but Land Registry search their house for £3. I try to make sure they are not in negative equity.
What should our criteria be?