As with any information that you retrieve in your research, it should be viewed critically to ensure that it is credible. Grey literature is often not put through the same quality processes a peer-reviewed resource is, and so evaluation of the source, author and contents is recommended.
The AACODS checklist was created by Jessica Tyndall from Flinders University Medical Library. The checklist includes the elements you should use when evaluating grey literature.
AACODS stands for
A - Authority
A - Accuracy
C - Coverage
O - Objectivity
D - Date
S - Significance
Tyndall, J. (2010) AACODS Checklist. Flinders University
Tyndall, J. (2008) 'How low can you go? Towards a hierarchy of grey literature'. Presented at Dreaming08: Australian Library and Information Association Biennial Conference, 2-5 September 2008, Alice Springs.