I had posted before about people reusing as postage used stamps but still see from public posts on Facebook that some people still do this illegal practice. It is fraud and these people who do it are con artists, in my book.
Came across a news page on a stamp dealer's site :
Operation Gum-Gum. A new generation of people are now unaware of the seriousness of such fraud. In 1989 the police, in association with Royal Mail, started an investigation under the name of "Operation Gum Gum". They built up evidence against a number of people who were buying kiloware, extracting unfranked stamps (and in some cases even cleaning off light postmarks), and selling them on to others. Those who were targeted found it a surprising and scary ordeal. Some individuals were arrested, some of these tried and convicted, and some ended up with prison sentences. For a while this had the predictable effect of stopping commercial activity in stamps without postmarks.