The intent is that "up to 50% or more", instead of being interpreted as "anything", is often interpreted as "most likely 50% with possibilities of taking it to the next level", and thus the advertisers try to get consumers thinking they could save even more than that (i.e. "at least 50% off" without having to say that and be bound to it). Does this really work? It must, because advertisers (particularly low-budget ones) keep doing it.
A fairly common variant of this now invoked by advertisements for cleaning products is that they kill "Up to 99.9% of bacteria". What this in fact means is that they could kill any quantity of bacteria from none at all up to 99.9% (including 99.9% if they meant "up to" to be inclusive), but they specifically won't kill all bacteria. Doesn't sound quite so good when you think about it, does it?note
A very similar thing happens with beauty products. Anti-dandruff treatments will tout that they will leave your hair "up to 100% flake free". A moment's thought tells you that so will anything else you try, including doing absolutely nothing.
You may accept the TV Tropes Wiki absolutely guaranteed pledge that you may save up to 100% of the purchase price if you don't buy the product.