I am sure you are not aware of this, but we live in a world where more and more prices you see are not set by human beings, but by computer algorithms. The price of petrol (gas) at the pump is more likely than not set by complicated algorithms that evaluate demand, oil price, season, historical events and several other soft factors to determine how much you should be paying.

Many online stores like Amazon relies on computer algorithms too. It is very clear from this ridiculous example:

For starters, why would you choose the Prime option if the discount has just been worked in to the base price? And then the big question - how on earth can they allow their algorithm to ask more for a used item than a new item?