Pouring Flairfactor Style
There is no " magic flair bartender pour spout " that we all use to entertain but not spill. Most bartenders who flair like to use a straight metal slow pour which has a small opening so that uniforms the pour making it constant and technically controlabble and is used in almost ever flair bartender competition I've ever been involved in but it will spill if you don't do the move right.
Having said that, there are many types of pouring spouts & systems out there that won't pour unless you push a button, put the bottle through a ring etc. but most flair bartenders use regular pour spouts and if done correctly will not spill. No one said it was easy but there are a wide range of moves that vary from high risk of spillage to very low risk.
If you are spilling then you are most likely doing a flair bartender move that either .. 1) cannot be done with that amount of liquid in it ( you really have to know what's possible and this comes with experience 2) you're doing too many rotation moves together in a row so even if you did have a low enough liquid level for one or two moves .. after a few the liquid will start to " creep up " the bottle and increase the odds of you spilling.