How would I know if a case has been sealed

You can and should run a background check. Look at the DCJS website. However, to confirm a case was actually dismissed and sealed, only the defendant can go to the clerk's office and check as they will not tell anyone else if it ever existed unless it wasn't sealed.

Go to the clerk of the court where the case was brought an ask for a certificate of disposition. That will tell you if the case has been sealed or not. You can also contact the DCJS and obtain a copy of your RAP sheet and see what, if anything, might be causing you your grief. I have included a link for you below.

You can: 1) run a background check on yourself through of Office of Court Administration; 2) Purchase a Certificate of Disposition at the court for $10; 3) Ask the Court Clerk's Office - if you are told there is no public record, the case is sealed.

The easiest and cheapest way is to go to the court clerk where the case was heard and purchase a certificate of disposition. If it was sealed, it should have a stamp indicating so. To make certain that this was done with the official record, you can request a copy of your criminal history from DOJ without an attorneys help. I have attached a link to my legal guide with the instructions.