When I read your comment above, I wondered if you'd gotten here by defining "fair" circularly.
And... yep.
And... yep.
I think consent and honesty make something Fair. Nobody has refuted this and The only other counter argument I've seen is that full disclosure would mean the seller gets more money. What is getting more money have to do with fair.?
[EDIT] I retract the "circular" claim—you're right that it's not that, it's the definitions of "lying" and "honest" that are making the difference.
When I buy a 20 cent bolt for my car, I don't tell them that it's worth $20,000 to me because my car won't run without it