You really should cut back on the coffee... =P

Huh? What do you mean? 

=D

But in all seriousness, I definitely wouldn't consider this a scam.

Think of it like going to a store that doesn't have a return policy. You expect to buy something for $10 and upon checkout it turns out that the sale is over and the item is actually $15. If you put you card in the terminal and enter your pin it is assumed that you're aware of how much you're paying and you agree to pay it. Now you could later go back to the store owner and say "I thought this was on sale, that's why I bought it. Can I have a refund?" and the store owner can give you a refund if they want but it is up to them. In a situation like this your best bet is to very politely explain that you made a mistake and if you could possibly have the difference refunded. A human approach will usually get you more understanding as we're all human and make mistakes, while fighting and demanding will usually get you nowhere in a situation where the owner technically did nothing wrong and has no obligation to refund you other than out of the goodness of their heart.

TL:DR
It sucks that you overpaid but this is not a scam in any way. If you rent a rig and don't check the price you're renting at you can still avoid the mistake by having a second chance to check before you send the money from your wallet to betarigs. If you miss both checks you can't go and blame the owner. Just try to reach out and politely explain your situation and hope the owner is in a good mood.

That's my two satoshis...