Genuine seller offer the stats right in 2nd round of discussion once he finds the buyer to be genuine, if the seller avoid doing so the buyer should just stop the discussion & move fwd.
Also I don't think that just keywords (unless it's a single keyword) or just some traffic increases a domain cost, it's a combination of both. There's nothing such called yesterday or today's model, basics for the business remain the same thought. It's just your and mine vision to do business keeps on changing.
For the buyer, he has to look for stats and then need to analyze it for the source of traffic, it validity & more importantly the scope of development the domain has and how much brandable can it be as it does really matters, as ultimately one day the domain has to be used for a website by an end-user.
On traffic faking issue, traffic can be faked but is not tough to detect as the buyer needs some basic analytical skill to check the traffic source.
While a domain receiving SE traffic is not bad if the traffic has been continuous & steady over a period of time as ultimately that would give better revenue from adsense than some parking stuff as due to SE traffic your CTR will be high and CPC will be good(based on the genre), repetitive traffic doesn't gives good returns.
Also if planning to buy a domain even for a small website once the SE traffic flows in you can use it to built the domain name as a brand as the user coming on a website/domain is far more focused and can be targeted as if the user gets what he wants he is going to come back maybe directly by typing in the domain name this time giving some valuable type-in traffic.
