The bureau told WSAU News/Talk in Wausau, Wis., it has received more than 200 complaints from customers who placed orders that were never filled with on-line seller TGSCOM Inc.
The Green Bay Police Department said it is working with more than 30 customers on potential felony charges of theft by fraud against the firm.
TGSCOM owner Eric Thompson told the Green Bay Press-Gazette that he is working to "rectify" problems and to find investors that can help him reopen his financially troubled dealership.
Over the years TGSCOM has sold guns and other merchandise to customers later involved in mass shootings.
A handgun purchased from his business was used in the 2007 massacre at Virginia Tech.
Thompson has emphasized all his gun sales were legal and he did the required background checks before making the sales.
Federal regulators have found TGSCOM in violation of firearms merchandising rules, including selling products improperly to underage customers.