DAVE SINCLAIR FORD DAVE SINCLAIR AUTO GROUP UNFAIR AUTO LOAN RATES !!!!!! SAINT LOUIS, Missouri

The ECOA has to do with discrimination, on things such as Age, Sex, Religion..etc.  There is nothing in there that says they have to use one Credit Report or scoring system over another.

But as for using your score, I can not remember a car or mortgage company using only one score to rely on for approval.  There may be some, but most I have ever heard of use the AVERAGE of all 3.  The reason for this is simple.  There can be different information on all 3 because not all creditors report to all 3 Credit Reporting Agencies.  So you may have a line of credit listed on only 1, or 2 of them.  There is nothing wrong with this, as there is no requirement to put a listing on your credit report.  The only requirement is that what is put on there is accurate.

I have a feeling that both dealers may be feeding you a line, in that they only pulled one, or only using one.  I would not be surprised that if you pulled all 3 of your credit reports you would see an inquiry on all 3 from both dealers(and possibly any banks they actually sent the application too). 

There is something else you probably should think about.  Some dealers use what is known as "spot delivery".  That is they give you a terms that are very favorable(such as 4.3%).  So you take the car/truck and a couple of weeks later they call you up telling you to come back to the dealer.  When you get back there they give you the bad news that you were not actually approved.  So in order to keep the car/truck you now must either accept less favorable terms(higher rate, higher down payment) or get a co-signer.  And while this dealer may not be doing this, the situation described sounds like a perfect case where it may happen.

On a side note, if you have such a difference between two of your three credit scores(you didn't mention your third score), you probably should see what is different on each.  Because there is often a minor difference between them because of what is reported.  But to go from the 500's to 780 there may be something incorrect.  If there is, it would probably be to your advantage to dispute the items that are incorrect.