In the US, we have a fairly new law, referred to as the "Stolen Valor Law", it has resulted in the prosecution of many of those who claim to be something they were not. It has also been a problem for collectors, as it forbids the possession of several of the higher medals awarded by the US Government (It has always been unlawful to buy or sell a Congressional Medal of Honor)
I live in a community that was founded by veterans of WWII and the Korean War, and many of my neighbors have done some very great things, but we seldom know about them until we attend their funeral, so I am always skeptical about some one who brags about their service. That being said, I have been taken in by at least one (possibly two) men who claimed to have done things that they have not, one was uncovered by the director of a museum that I work with, the other, I have lost contact with, but I do know that he did do much of what he claims, but there are some memories that do not match up with history.
US service records are so bad, that is is difficult for a veteran of WWII to get benefits they deserve, but it is possible for some one to forge documents to get these benefits, the new law has made it possible to prosecute some of those who have been discovered.