Are you wondering if that piece of Indian jewelry or that basket you bought while traveling through the south, is authentic Indian art work...or any piece of Indian art work you might purchase...
Another way to determine whether or not an Artist is Native American, if you know the tribe, call their Tribal Registration office and ask....:) Not sure they all have a formal type of registration office but someone in the tribal office will either know them or their family. Most tribes have a web site and make sure you're not dealing with a fake tribe! The DOI/BIA has a website that lists all the recognized tribes as well.
You'll find Tribal staff more than willing to help you and they are very cordial to work with!!
Just ask...it's that simple!