There are two main kinds of spurious degrees:
1. Obvious forgeries made by people who think they are computer graphics experts, and who often work from a back alleys in the Kao San Rd area of Banglaphu (the backpacker district of Bangkok). Some of the certificates look quite good, they even have the embossed red star seal. However, the paper is not watermarked, and there are often obvious spelling mistakes, or the university crest has been scanned back to front. A classic example was the one from a university in Liverpool. I had four job applicants with it in one year (2006).
2. Degree mill certificates. These are the ones from those websites that promise you a degree based on your previous working experience, and from universities whose registered address is on some tax haven island such as some of the BOT. There are USA and UK government blacklists of degree mills, as there are USA and UK lists of genuine accredited universities. Some of these mills will promise verifiable certificates from renowned universities, but I won't go into detail here how this scam works.
Serious employers will almost always ask for a transcript and some will insist on a transcript in a sealed envelope. All genuine universities will confirm the degrees of their alumni, but probably not by email, as even emails can be easily faked. The employers who discover one are unlikely to take any legal action, they just won't hire. However if they do hire a teacher and the fake is discovered by one of the many government agencies for visa, work permit, and teacher licence applications, the consequences, particularly in Thailand, can involve a few nights in jail, and expulsion from the country. Such cases used to get a mention in the press, but they are so common now that they are not considered newsworthy. The 'Bangkok HIlton' and the immigration nick are a places to stay out of, even if the teachers are able to stay out the Bangkok Post.