I've checked the Equifax report for both of us, and they are nearly identical, except for the paid collection noted on my wife's account. We have low credit utilization, about $600 on one card with a $4,000 balance, three other cards are clean (around $12,000 in total availability for the 4 accounts).
The finance manager at the dealership is the one who showed us our scores before they hit the shredder (he wasn't supposed to, apparently). The rest of the story is we ended up with another lender they use with a shorter term, but just as good a deal. Still, I was annoyed enough to try to figure out why the discrepancy, and the Equifax reports are identical enough to not justify the difference. So i'm still stumped.
The finance guy did tell me that all the credit agencies have come up with their own scoring systems, that they vary widely between them, and aren't worth a darn when compared with an actual Fair Isaac FICO score.