Sorry, I took your calculations to be those presented to you by Midwest as a basis for a calculated settlement. Another post contains language that suggests that Midwest purchases small lots outright. If that’s true, your calculations are not material to the sale because you accepted a cash offer for the item.
I retract my advice to keep your gold. I do recommend that you consider the cost & risks associated with transacting business in small lots with strangers as you decide whether an offer is too good to be true or not. Sharp operators looking for rubes abound, and there’s lots of ways to drain you of valuables that don’t involve breaking the law. Sharp businesses rely on said rubes not reading — or reading but not understanding — the fine print and getting distracted by pictures of piles of gold and “You’re getting paid, Boss!” memes.
Play fair, be suspicious, and walk yourself through why you believe what you believe when you think you’ve been wronged. I think you didn’t get what you wanted or expected, but did you get what you bargained for? I suspect that you did. Consider the $80 a cheap, hard lesson. A really, really, really cheap lesson. If you fail to learn the right lesson, the remedial lesson may cost you much, much more. You’re not going to change Midwest Refineries or any other multi-million dollar enterprise. Do something else. I think you got lucky that you didn’t get disappointed to the tune of $5k for failing to read the terms. It happens every day. Good luck, seriously.