A faxback scam is an unsolicited fax that can offer you anything from amazing diets to fantastic deals, business directory entries and competition entries—all you have to do is send a fax back to a premium rate number (starting with 190). Premium rate faxes can be charged at more than $6.00 per minute. The scammers make sure your fax will take several minutes to get through, resulting in hefty, unnecessary phone bills (a single fax could cost you $20 or $30).

They usually target small business, often with offers of directory entries and catalogues of goods and services.

Warning signs

Hope the information is useful to you.
Cheers!
Patrick