Because if the seller gets an inkling that he has an overly enthusiastic buyer, the seller may get cold feet if he thinks it is underpriced and the sale will collapse.

OP is playing the game just right by not appearing too eager. Asking for some pics so that the machine isn't totally misrepresented is a good first move with some follow up additional generic questions on functionality with nothing too overly technical or game specific that will get the seller's wind up him by thinking you are a buyer looking to flip it.

If the machine isn't advertised elsewhere publicly, this method will always work in a buyer's favour.

And in answer to the OP's question, even in parts alone it is worth it at that price, but in order to keep playing the game if you were subsequently inspecting it in person I would follow it up by making an offer of $350 on it anyway.

In the seller's mind, this is a non-working machine that needs new boards.

Worked out well.

Should clean up nicely.