When Turtledude goes onto the local Jr. College and shoots and kills dozens the investigation may very well lead to you. Then, you ought to be complicit and put in prison. And, since you had a duty to perform the background checks and did not do so, and harm was caused, you will lose everything you own, home, car and all of your guns.
Now, it may be hard to prove "beyond a resonable doubt" and put you in prison (where you belong), but the standard of proof in a civil suit is much lower, and everyone effected by your irresponsible behavior will sue your ass. Attorney fees alone will put you in the poor house.