I found a dissertation that's perfect for my research. The author covers exactly the gap I'm trying to address. The only problem: it's a dissertation. Not a peer-reviewed article. Not a book from a university press. 
My advisor says: "Dissertations are fine to cite. But they're not the gold standard. Use them carefully."
What does "carefully" mean?
I asked her to clarify. She said: "Dissertations haven't been through the same peer review process as journal articles. They might contain errors or unsubstantiated claims. But they also contain original research that hasn't been published elsewhere."
So... use them but don't rely on them?
I found a study in a dissertation that hasn't been published anywhere else. The data is exactly what I need. Can I cite it?
Another professor told me: "Cite the dissertation. But if the data is central to your argument, try to verify it somehow. Contact the author. Find similar studies. Don't build your whole argument on one unpublished source."
That seems reasonable. But also... that's a lot of work.
What's the norm in your field? Do people cite dissertations? Or is that seen as amateur?
My advisor says: "Dissertations are fine to cite. But they're not the gold standard. Use them carefully."
What does "carefully" mean?
I asked her to clarify. She said: "Dissertations haven't been through the same peer review process as journal articles. They might contain errors or unsubstantiated claims. But they also contain original research that hasn't been published elsewhere."
So... use them but don't rely on them?
I found a study in a dissertation that hasn't been published anywhere else. The data is exactly what I need. Can I cite it?
Another professor told me: "Cite the dissertation. But if the data is central to your argument, try to verify it somehow. Contact the author. Find similar studies. Don't build your whole argument on one unpublished source."
That seems reasonable. But also... that's a lot of work.
What's the norm in your field? Do people cite dissertations? Or is that seen as amateur?