If it was functional I would say scam. Since it has a faulty logic board I would be wary but this may be legitimate.
The owner may just be trying to recoup some money and does not know what a defunct unit is worth. However I would meet in person and check for physical damage and test what you can; does the screen power on, drives spin up, battery indicator show a charge.
If the case is physically damaged don't even bother as other components could also be damaged. Now if the damage is from water, assuming the seller is forthcoming, then there may also be further damage. Assuming the repair is simply a faulty motherboard that is no longer under warranty this could be worth it if you are willing to do the repair yourself and scour ebay for a cheaper replacement then through a normal e-tailer.
Even if the repair is not worth it for you. Assuming the other parts are good you can disassemble the Macbook Pro and sell the components on eBay for a profit.
All in all I would call, set up a meeting in a safer environment like Starbucks and check it out.