If there is a big difference between the initial interest rate and the APR listed in the ad, it may mean that there are high fees associated with the loan.
Pull your credit report from the bureaus and review it for any negative items (late pays, collections etc) and inaccurate detail. Try to dispute negative items and remove them from the report. If required pay off any unpaid debt. Otherwise, you won't get a low rate and may not even qualify. Of course there are lenders in the subprime market who may offer you a bad credit refinance loan, but it's better to avoid them as they'll possible charge higher rates and fees.
Be Inquisitive. It's your responsibility to make sure that you understand the terms of your loan. Ask questions and listen carefully to the answers. Don't sign your loan documents until you are satisfied with the information and confident that you have made the right decision.
Be Prepared. You'll probably be asked for more information and documentation after you submit your application, but before your loan is approved be prepared to document your income and assets. Answer any questions and fax documentation to your loan representative as soon as possible.
You can ask for a copy of your settlement cost papers (the HUD-1 form) one day in advance of your loan closing. This will give you a chance to review the documents and verify the terms.
