I'm going to buy an item absurdly cheap because the person doesn't understand it's value
What type of item is this?
It's an antique item, it's worth a thousand dollars
If you know that it's worth a lot more then they have it listed at then there is nothing wrong with trying to use your knowledge to get an item of value for cheaper then it's worth. The seller should know what they are trying to sells worth before listing it.
I feel like I should value morals over the money but it's such a good deal.
Like I said. There's no reason to feel bad if the person has it listed at that price. if it was someone you knew or at least spoke to I could understand being hesitant but there's nothing wrong with leveraging your knowledge.