Tim Wenzlawsh is an avid gun collector who thought he found a great deal online. The collectible was 20 percent less than the going rate, so he quickly contacted the seller by phone.

"This guy knew his firearms," said Wenzlawsh. "He knew what made them collectibles."

Wenzlawsh was eager to get the item before it got away. So, as requested, he sent the seller a postal money order for $1,000.

"I hadn't heard from him in 4 or 5 days so I tried to contact him and the number I had went straight to voicemail," said Wenzlawsh. "I emailed and kept doing this for a few days afterward and just nothing ever came of it."

Wenzlawsh had been duped, but he was not alone. Postal inspectors were already investigating dozens of similar complaints.

"In every case, the person bid on this item but never received their item," said U.S. Postal Inspector Alexandra Papageorge.

Investigators soon realized all of the complaints were actually against the same person, Paul Steven Webster, who just kept creating different accounts.

"He would get about $10,000 and so many victims, then it would get shut down, then he would re-create a new one," said Papageorge.

Inspectors said if you send a Postal Money Order, require a signature from the recipient. That evidence was invaluable in tracking down Webster. He pleaded guilty to one count of mail fraud.

Postal inspectors warn consumers to always be cautious and protect themselves when conducting financial transactions online. Tracking numbers are a good example of documenting the transaction.

"I had a tracking number, I had a signature for who signed for it… and I could actually research that mail and where those payments went to," said Wenzlawsh.