Toss the ball vertically up 16cm or more from a stationary open palm and make sure your opponent can see it from the moment you release it until you strike it.
This is the simplest description of the correct table tennis service I can think of. Although as an interpretation of current rules it is not quite complete, it would make the majority of services absolutely acceptable. And yet every so often we see a service that fails even this basic description. Call it a let, a loss of point? Maybe ignore it? What to do if it's a game point or a match point?
Those questions are not easy to answer. According to the official ITTF Handbook, executing an incorrect service leads to the instant loss of a point (fault) although an umpire may choose to issue a warning when the error occurs for the first time. It seems simple enough but enforcing such principles at the local level could lead to a serious argument.
Understanding "The Laws of Table Tennis" (ITTF Handbook, Chapter 2) and ensuring serves are correct is important. We don't have impartial, professional umpires turning up at our local league events. We play and we umpire alternately. No one wants to upset anyone else, therefore rules governing correct service are often not enforced. It seems the only way to address the problem is to raise the awareness and perhaps encourage club members to assess their own individual serves. Why not ask your practice partner to check if you're doing it correctly. Let's bring it to the surface, talk about it and train accordingly. At the end I'm sure everyone participating in the league strives to win his matches in an honest way. Fair play, that's certainly what most players look for.
Table tennis is a game where hand - eye coordination plays an important part and serving is no different in that respect. Without training, players may find following rules of the game challenging. And of course, developing a high quality service takes months or even years of practice. Can you start tossing the ball near vertically if you've never done it before? Or would it affect the quality of your services if you were asked right now to toss the ball from an open palm of your hand? Are you aware where your free arm is once the ball is up in the air? You can start improving your skills any time, why not now? It is absolutely possible to develop an excellent serving technique that is beyond any controversy.
The good news is there is a growing range of training materials available online. A quick reference guide provided below is a good source of information on the subject. It's based on ITTF Handbook 2017 (2.06 The Service) and some of you probably have seen it before at ADTTA tournaments.
Also, since July 2016, table tennis umpires have 7 brand new hand signals to communicate with players with regards to fault serves. These are already in use during international events. Luckily for us, people working on the hand signals idea developed a very practical guide. I'd highly encourage everyone to check the document provided below. It comes together with a video material (no audio though) which provides an excellent, detailed visual description of all instances where requirements of the correct service are not being met.
Hope you found this article useful. I'd like to wish you all many outstanding wins and an entire range of quality services that are absolutely 100% legit.