You have to go to a testing center and show two forms of ID before you are allowed to take the test. You are also monitored during the test and cannot bring anything into the room. They even require you to turn in the scratch paper and pencils they give you after the test is over.
If they can successfully do this it's interesting because Amazon must have a great interest in ensuring there are enough competent people to make best use of AWS to avoid a choke-point where AWS wants to expand but the shortage of talent raises costs.