Off the topic, but let's say you purchase a firearm from a private individual at a gun show. No paperwork, cash only. After the gun show, you realize the SN has been obliterated from the firearm. What's the best course of action - turn it into the local police dept and write it off as a loss?
Toss it into a dumpster, duh. Kidding aside the best course of action is probably calling the local ATF branch and get ready for a serious case of buyer's remorse. Most firearms have an easy to spot serial number but some handguns could have the number concealed by the grips. Something like a Browning HP that has the serial number on the front strap could be hidden by wrap around grips. You might not think about it if you weren't familiar with that particular firearm.