I've read countless posts on various boards about how frustrated folks are with using their machines to cut fondant or gumpaste and i can appreciate their 'pain'. I was thinking about this and then realized that it all comes down to the one BIG variable - the material being used. In fact the only variable is the fondant/gumpaste which unfortunately can vary a lot and thus cause a lot of problems.
IMHO success or failure is completely related to the texture/thickness/firmness of the fondant/gumpaste. So that is the 'trick' - finding the right combination which will very a lot based on brand of fondant/gumpaste used and the type of microwave used to 'soften' it because the wattage and thus power levels vary (if you even need to go down the road of microwaving it...sometimes you do and sometimes you don't).
So having said that there is a lot of trial and error - which I know doesn't help too much.... the only thing you can do is look for 'clues' as to what is wrong... if the blade is pushing the fondant and making it move (and by this I mean actually moving a big chunk) - think icebreaker going through ice - the fondant is probably too hard/stiff.... if it is making it crack (again think ice breaker) it is too hard/firm... if it is pushing up little ruffly edges as it cuts (on either side of the blade) it is likely too soft...if it creating little puckers or ruffles in front of the blade as it cuts it is likely too soft ..... well at least that has been my experience.
If you watch the various CHA videos online or other videos on youtube that show fondant being cut pay attention to the texture/pliablity/firmness etc of the fondant AS THEY LIFT IT off the mat AFTER it is cut - that will give you something to aim for..