I was asked at the NEHGS library how to tell a reliable compiled genealogy from one that may not be so reliable. I had the great experience of being a novice genealogist before the Internet, when you went into a library and soaked up the knowledge of the librarians and genealogists. And I got to do it at the NEHGS library of all places. So I learned the good sources from them. So, I pondered for a bit how to impart such information.
I had two main points to tell the patron. First, I pointed them to the list of fellows of the American Society of Genealogists. I said anytime you these names as an author, it's a genealogy on which you can rely. Secondly, I said that if a modern genealogy (say one printed after 1985) has footnotes for each event, or at least endnotes that are to primary sources, it is probably reliable also. This doesn't mean that compiled genealogies that don't fall in either of these categories are not well-researched. I'm talking about reliability, or if you will, faith that I needn't redo someone else's research.
All genealogists are human and one can find errors in all works (if you look hard enough). Also, genealogy can be all encompassing and we all have to draw lines somewhere or nothing would ever get published. Sometimes we are just one generation away from a connection or one female generation away. However, as I noted in this posting, we have earned a bit of rest from finding every single original source. I'm confident I don't need to do anything on the Whitneys in Watertown, because Melinde Sanborn did a bang-up job on them. And there's a long list of other people from whom I descend, I'll never bother to research because I trust the research of other people. Those other people is a very short list for me, but it's still there!