An important piece of info is before you enter into any financial arrangement you should know what your credit score is because some lenders will use the fact that most people don't know their score as a means of bargaining.
They might tell you your score is lower than it is to help squeeze a higher interest rate out of you when signing up for finance or they might even start their negotiations with comments that you won't get credit anywhere else due to your credit score. This gives them the opportunity to charge you more if you believe them and think they are your only option.
Any way that a lender can get a few extra points of interest out of their customers can add up to a good increase in their profits at the end of the year so they will be using all the tricks they know to get higher rates where possible.
If you come armed with all the information they will know that you are 'financially aware' and you will be less likely to be tricked into something that will cost you more money.
It might be worthwhile to let the lender talk about your credit score before you produce your information as this will be a good way to decide whether they are trustworthy and whether you want to do business with them.
If you have a reasonable score you can ask them for better rates based on the information that you have. Remember that even a slight decrease in interest rates can save you a lot of money over the course of a loan and the money is always better in your pocket than theirs.
Reputable lenders will give you information that matches your own and if it doesn't you should ask them why not and see where the variances lie.