Not really the right term IMHO. Instead of calling a return which implies ROI, it's a discount. If you did sell it at the higher price and notwithstanding taxes, overhead of inventory management, other costs and your make 27% then it's ROI.

Isn't that how it always works at Costco? If you buy in bulk - you save.

I agree, if you buy in bulk you save. And I agree typically, people associate return/ROI lingo with investment. However, I think it's useful to think this way to compare ways to utilize your excess money. I find it helps people think about where they can do this in their lives outside of the normal Costco run.

If I were to make a list of tat post from hacker news this would be on it.