Don’t confuse the use of FindAGrave as a source with use of the citation for FindAGrave.
The citation as provided from the new site is excellent. It identifies where the information was found (the repository Find A Grave, database and images (https://www.findagrave.com :), how and when it was found (accessed 9 November 2017), who it pertains to and what was found (memorial page for John H. Sands (29 Sep 1861–27 Jan 1940), Find A Grave Memorial no. 62272987, citing Deepwood Cemetery, Nevada, Vernon County, Missouri, USA ; Maintained by JARROTT P. COX (contributor 46518980) .)
This gives sufficient information so that you can review the FindAGrave entry to assess the quality of the sources. These vary widely, some describe census or marriage records, some have death certificate images, some are obviously put together with cemetery records, most give you hints for names, dates and locations to search for records, and some are just a pretty good indication of where someone is buried.
A blanket statement that FindAGrave shouldn’t be used because it’s not reliable is like saying that WikiTree profiles shouldn’t be used because they have no sources or are just someone’s online tree. (Aside, in looking at unsourced profiles, I’ve found quite a few where the family aligns with FindAGrave, and from there have been able to find marriage and census records for those profiles.)