I think i was also told by Sedo that nameserver forwarding is picked up more by SE than URL forwarding, i don't know the reason. It would be interesting to know if anyone has tested the options.
I would be hesitant to approach the person or agent of the name offering to sell it, I would think this would provide them with good evidence of bad faith, just my 2 cents
I have found the tool sometimes helpful as an extra step for verifying traffic, used with other tools you can take a look at the past development and work out whether the traffic stats the seller has sent you seem to be inline with the past developement of the page.