Boston — With the Boston Celtics making a deep run in the NBA playoffs, transit police are warning fans to be careful when buying tickets from secondary sources.

Massachusetts Bay Transportation Authority police in a statement posted on their website said they have received reports in the past from people who have purchased counterfeit tickets that were advertised on sites such as Craigslist or Reddit.

The person selling the tickets will often arrange to meet at a busy MBTA station, then as soon as the money is handed over, disappear into the crowds before the buyer realizes they have been duped, police said.

Celtics fans should only purchase tickets through authorized and reputable ticket agencies, police said.

The Celtics play the Miami Heat in Games 3 and 4 of the Eastern Conference finals in Boston on Saturday and Monday.