Lots of CarSpace members have reported that the dealer has showed them the "real" invoice. All you have to do is ask. Of course, sometimes dealers dummy them up and offer to show them to you.
But that still doesn't account for holdback, much less bonuses, free training. cruises, free demos and "executive" cars, free advertising, priority model ordering and who knows what other spiffs the manufacturer or distributor is offering this week. Sell more cars, get more spiffs, and lower your unit cost.
Oh, and then there's the extra interest the F&I department can pull off the top, plus other kickbacks the banks and financing companies toss in, plus kickbacks from the extended warranty and mop & glow companies. The salespeople don't know how much most of this stuff adds up to.
And then there are warranty audits and work may get charged back against the outstanding invoices or holdback if the dealer can't justify the work that was done.
I bet the owner doesn't even know how much a car costs until the accountants close the books every year.