Many players can put good spin on their serves, but it is obvious what type of spin is on the serve from your racket direction. There are many ways of hiding the spin, but here's a simple one: the instant after contact, change the direction of the racket, and exaggerate the follow-through – but in the "wrong" direction. So if you are serving topspin, you might use an exaggerated downward follow-through to make it look like you served backspin. You might also try following through to the side to disguise backspin or topspin. One classic, and perhaps the most common, is to serve no-spin (by contacting the ball near the handle, which doesn't move much), but exaggerate the downward motion (especially with the racket tip) to make it look like backspin (so they will often return it high, giving you an easy put-away). Remember – the hand is quicker than the eye, and serving is the "trick" part of table tennis.