I would pay, load it up, and then give the seller some extra cash.
I would load it up first so the deal does not go south before the game is physically mine, but then I would toss them a bonus later.
I actually like random acts and think painting perceptions is fun. That said, maybe if I bought a nice MM for 1k from a nice but iggnorant person I would likely do something else nice for them in return. Maybe annonymously pay for something around their house to be fixed or a cleaning person to come give them a hand once a month for the next year? Basically, they were already happy to sell the game for what they thought was fair so why ruin that perception to where they realize they left a good chunck of $ on the table and then feel salty... Instead, make them happily suprised when a nice gift shows up at a later date.
