[misterbwong]

I'd argue there's a qualitative difference between A/B testing regular pricing vs. testing via targeted discounts.

If your friend finds out you got a "private sale" price, this doesn't seem to violate the "fairness" principle because you were a part of something or got targeted for a reason. It might actually end up increasing the friends FOMO/jealousy and get them to find ways to join in on the discount via mailing lists, insider clubs, etc.

A/B testing pricing might come off as arbitrary and not easily reasoned away thus violating a sense of fairness (at least during testing).

I don't see this as a huge issue as A/B testing is usually limited time/scope but something to think about, I guess.