When I was in the academy a decade ago, the instructors gave us about two dozen ways of fucking with someone doing FSTs that would look okay on body cam but make the tester fail, to give more weight in court.
Any lawyer worth their salt will tell you that unless your local laws require you to do FSTs, you should refuse them. Fuck anyone actually driving intoxicated, but if you get pulled for DUI you're getting railroaded whether you're sober or not, so you should defend yourself in as many ways as the law provides.