A retip is actually the substitution of the existing cantilever/stylus combo with some other combo. The manufacturer produce them as a complete unit. They are than put in the tube behind the cantilever and glued.
This seems to be more easy to do then to glue the stylus
alone in the existing cantilever. In the aluminum cantilever the stylus can be 'pressure fitted' which means that the use of glue can be avoided and a better connection
between the cantilever and the stylus achieved. By the so called 'exotic cantilevers' (boron, ruby or sapphire,etc) the stylus can be only fitted with glue. As Syntax already pointed out the quality of the styli is very important.
That is to say not only the stylus shape but even more important the quality of the diamond and its manufacturing (polishing,etc.).
Raul has the most experience with retipping so I hope he will contribute to this thread.