The big problem with spot fixing is it is really hard to do something amazing, like knock the timbers out of the ground with a searing leg stump yorker in the 3rd ball of the 8th over. Or step down the track and hit one into the sight screen in the 1st ball of spin in the 20th over.
You can only really bet on something crap – a wide, blocking an over out or a no ball being bowled (followed by a some hammy acting about the turf in the best drained ground in the world being a bit slippy, and needing some sawdust).
Unfortunately test cricket, the purist form of the game, is the most likely to be affected. A no ball carries no penalty other than a run, maidens are frequent