Yes, make sure they are using a small brush to edge near the garage and sidewalk areas. If they are spraying, make sure it looks very thick when it is being sprayed. Spray-application of sealer always looks thicker than it dries too. Also, if they are using a squeegie or brush, make sure that there are no streaks, there is no excuse for streaks along your driveway.
If you want a high-quality and durable seal, ask if they are using sand in their sealer and if so, how much. Two coats is the standard for most areas in the United States. Sometimes if there is a lot of snow plow or other abuse on the drive, you may just want to do one coat about twice as often.
Ask if there are any guarantees, at least one year should be on any good company's sealer.
Also, do not turn the car or truck tires on your driveway for at least three weeks after it has been sealed. It can take around 21 days for it to cure properly, so you may leave some tough spots on the driveway if you do that before it is cured.