Robin, Find-A-Grave allows "Virtual Cemeteries" as in cemeteries where you can add people. For example,
http://www.findagrave.com/cgi-bin/fg.cgi?page=mr&MRid=48186744 has several. I have a couple of private ones set up for Wrong Cemetery or Wrong Information. If you mean fake cemeteries, like several of these,
http://www.findagrave.com/cgi-bin/fg.cgi?page=csr&CScn=Saint+Vincent&CScntry=4&CSst=20&CScnty=1144, it's bad enough Find-A-Grave officially made two of each of the numbered ones as noted in the cemetery notes, but there are a number of unofficial duplicates like
http://www.findagrave.com/cgi-bin/fg.cgi?page=cr&CRid=2541135 Also seen fake ones or ones created because the obit or death certificate either used a vague cemetery name (Wichita Cemetery, CIty Cemetery, etc.) or misnamed the cemetery. In his obit, my uncle is listed as buried in Lovisa Street Cemetery in New Orleans. A later obit mentions St. Vincent de Paul #2 on Louisa Street. I haven't added him because I don't know if that translates to #1 Louisa Street or #2 Sonia Street on Find-A-Grave.
I don't rely on headstones photos as a safe source as I found several where the headstone is correct, but the person added them to the wrong cemetery in the wrong county. Maybe they got confused as to which cemtery they were in when they took it or they crossed a boundary and didn't realize it was a different cemetery. There are several in town next to each other and there may not be a notice you switched from being in cemetery A and you are now in cemetery B. Gets even more fun if they used GPS and the GPS is off enough to put them in a nearby cemetery.
Cemetery records can be off. Meet Mary Gates,
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=33258710 Buried in 1911 in Maple Grove. Between 1915 and 1918, she was dug up, moved to Los Angeles, move back to Maple Grove, dug up and moved to Salt Lake City, and finally re-buried for the last time in Maple Grove. When I first checked with Maple Grove, they said she wasn't there. After additional research, I was able to verify with a plot location. Turns out the cemetery assumed her last burial was her death year until I asked them to check. Highland, which is across the street from Maple Grove, kept such poor cemetery records there is no way to know how many missing burials weren't recorded. It is estimated as many as 200 - 2,000+ aren't recorded in the cemetery records.
A local graver has over 110,000 memorials he added. The first 80,000 were added through walking the rows or from cemetery records for the unmarked. The last 30,000+ are from obits and these are the ones I find are most likely to be in the wrong cemetery.
Somebody added my cousin to a V.A. cemetery. From the V.A. website, he's not there, but someone with a similar name who died four years later is buried there. I called the cemetery and verified he's not there. For now, I haven't requested a cemetery change as I don't know where he is buried. I expect he's probably on his widow's mantle if he wasn't scattered across the mountains of Colorado. I am trying to find an alternate way to determine for sure as I don't know the widow well enough to raise the question.
I treat all of the memorials as I do trees on Ancestry - a possible starting point which may or may not be accurate. I had a great example where the wife remarried and her headstone didn't match the name (Sarah C. vs. Carrie with her last married name as listed on cemetery records), but looks like the memorial manager went ahead and changed her name to match the headstone. The downside there is people who only knew her by her last married name will no longer find her on the website. Or Bettye Benson
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=112111963. If you didn't know she had died a Benson, you wouldn't find her on Find-A-Grave as her maiden name isn't listed even though it's on the headstone along with the last names of all five husbands she outlived.