If one of your key metrics is rate of returns, surely this would show up in an A/B test. You could also check for it in usability testing by making the task something where the user would be interested in the "fine print details" if they were visible enough for the user to notice.
A UI for creating a shopping cart. We can rank two different variables here:
1) Number of users making a purchase. 2) Number of users returning goods because they didn't actually want it.
If we focus only on the first option in our user testing (as any shopping cart user testing will do), we will generally make the 'fine print' descriptions of items as small as possible. We will make it very easy to buy an item with a single click. This is going to give us the best 'purchase rate', guaranteed.
However, we are going to get increased returns as users will miss important product details. We will get lower 'user happiness' with our store as users will feel a bit cheated and have to turn to external sites for more information. In the long run, users may stop using our store entirely and our purchase rate will fall.
This is a classic example of 'short term' or 'greed' based optimization. I feel nearly all UI testing I've seen does not cater to variable B - only to variable A. Catering to variable B isn't even really possible with a UI or A/B test?