Scratch is, by definition, zero handicap but both amateur and pro golfers can have plus handicaps. Ian Woosnam used to play in club tournaments at Oswestry with a +4 handicap and, famously, won a monthly medal with a gross score of 57, a net score of 61.
Scratch is much better than "decent". I'm a 12 handicapper and I've played with scratch golfers and pros (including Erik van Rooyen). The balance, clubhead speed and ball striking ability of scratch players is in a different league to decent players (say 4 handicap upwards). The difference with...