1. The police had no valid reason for stopping you.
The police are prohibited from pulling over private citizens arbitrarily without reasonable suspicion. Officers of the law need to have more than a "gut feeling" that a particular person has or is committing a crime, as a precaution to keep law enforcement as an objective process.
So in the context of impaired driving, police should see the suspect doing something wrong before they can be pulled over. That means if you were following the speed limit and traffic laws, and that you were not swerving, then you can probably assert that the police officers had no reasonable suspicion for stopping you and thus any evidence obtained may be rendered inadmissible in court.
2. The tests were done incorrectly and samples were not stored properly.
The police are required to arrange a proper blood-alcohol test performed by a licensed phlebotomist following your arrest. If the wait times took too long or it was an unqualified lab technician who conducted the test, then these details should be cited as a part of your defence. Blood samples should also be stored and maintained properly to avoid contaminating or altering the results, and the sample can be thrown out if questions arise around its integrity.
3. Field sobriety tests did not follow protocols.
There are guidelines to be followed when administering field sobriety tests (FSTs), and if law enforcement do not comply with such protocols, then the evidence may be rendered inadmissible if the officers were overly intimidating and disrespectful.
4. You have a medical condition.
Sometimes, a medical condition (or its treatment) can make a person appear drunk, even though they aren't technically over the limit. A health condition or the drugs being used against it can even affect the results of a breath test, somewhat complicating matters. Examples of such conditions include sinus troubles, allergies, neurological problems and fatigue, while diabetes can also produce an "alcohol smell" due to glucose fermentation in the blood. If you are currently suffering from any medical issues, you should therefore inform your lawyer immediately.
5. Law enforcement and prosecutors attempted to entice you with a plea bargain.
By law, prosecutors cannot interrogate a defendant without the presence of his or her counsel (or without consent). Nevertheless, police officers and district attorneys frequently attempt to entice defendants with a plea bargain to avoid the hassle of a trial, often leading individuals to entering into a plea without being fully aware of its implications for their situation. Judges will probably overturn any pleas entered outside of due protocol.
A DUI charge can be a complicated matter, and establishing a strong defence is critical to lowering or possibly dismissing your case. Although the burden of proof is the prosecution's responsibility and they need to prove you're guilty beyond reasonable doubt, you still need an impaired driving defence lawyer with extensive experience in dealing with such matters. By raising reasonable doubt to your benefit, a skilled lawyer will go the extra mile to defend your rights and protect your future.