By sticking to regulars a guy may get a 90% positive rate - but even with regulars, it'll never be 100% - she may have hit her big toe that morning or had a fight with her mother on the phone 5 minutes before you arrived. There are, literally, a thousand different things that could cause a woman to be in a bad mood.
I have a 75% positive rate and I salute those guys who achieve a 90% rate with WGs - but any claim above 90% is well into Alice in Wonderland territory.