Discounts based on users

Hello,

i'm trying to add some more dynamic aspects to the site. What I'm wanting to do is make a person create an account with us before they are able to make purchases. I was able to create all the pages needed (pretty sure) in the security assist wizard. In the table that was made in the database I added a custom row labeled userapproved which will just have a simple true or false value assigned to it.

Here's what I'm trying to figure out... If the user that is trying to check out has a false value assigned to it, then the person will need to pay full price for the product. If the user has a true value assigned to it under userapproved in the database then I want them to have a 15% (for example) discount on the product.

What I'm not sure how to do is during the checkout process, I'm needing the site to first check to make sure that the user is logged into the site. Then I'm needing the site to check for userapproved in the database to see if it has the true or false value, and make the appropriate adjustments to the price of the books if needed.

Thank you