Service tutorial video by one of the best server in Japan.
Will add the translation if anyone is interested.
1:15 For Topspin serve to look like backspin, the racket needs to start higher than the ball at the back swing. During the downward motion, cock the wrist to lower the racket head then uncock to impart topspin at the contact.
1:27 *Topspin disguised as backspin
1:53 Disguise it as backspin with scooping motion at the follow through.
2:23 *Backspin disguised as backspin
2:30 *Backspin disguised as topspin
2:41 For backspin server to look like topspin, start the racket from below the ball at the back swing. At the contact, cut the ball then have upwards follow through.
3:07 Vertical racket angle at the impact and swing from up to down.
3:13 As little downward follow through as possible to disguise it as topspin.
3:30 *Topspin disguised as topspin
3:52 Tactics: If the opponent swings hard, I tend to use topspin serve more. Vice versa for backspin serve.
4:19 *No spin
4:56 Tilt the racket forward so that the service looks like topspin.