Recently, searching for "W" fare in order to apply 40PP upgrade rather than 80 for HKG-SFO roundtrip, the site gave me a Basic Economy ticket in W booking class. I found out only after the purchase but thanks to the 24-hour free cancellation I was able to cancel. This is the first time I encounter this. An example is like this:

City pair Fare class Fare basis code
HKG - SFO W WLWNNJBI
SFO - HKG V VLWNNJBI