For sites with big ticket items where the transaction doesn't take place online, it can be trickier to try and attribute the sale to a certain ad campaign.
How do they do it? One method I can think of is to show different phone numbers for users that have been cookied as coming in from different ads.
We actually found another vendor that does this on a per visitor basis (ie. each visitor gets their own tracking number). While I think THAT is overkill, the technology is there to do this kind of thing without too much overhead.
The more sticky situation would be phone calls if you have a number.
Although using this method doesn't directly attach sales to conversions, it seems it would help qualify leads a little better and hopefully maximize you Adwords spending.
For example, send incoming customers to a survey. Pay $1 for customers who self-identify as non-profit or academic, $10 for customers who identify as Fortune 500. Google will go off and determine if it's more efficient to deliver you 10x non-profit customers, or 1x corporate ones.
Folks who have tried something like this, does it work?