Thanks for the reply.
None of the ovens that I have been able to find offer any kind of certification unfortunatley.
-However, the Earthstone offers a 5 year limited warranty.
-The Woodstone offers no guarantee or warranty. However, they claim that within the 10 years of their existence every single one of their ovens are still up and running. They are also used in highly commercial high volume restaurants such as Wolfgang Puck, California Pizza Kitchen, Carrabas, and in Universal Studios.
-The Acunto oven I spoke to Gianni Acunto over the phone and he said his ovens never break down and was willing to give me a guarantee for as long as I wanted.
-The Forno Bravo and the Ferrara Ovens I'm not sure as to whether or not they provide any kind of warranty or not.