He came to some big city posing as a successful businessman seeking investors for some new enterprise. He would give as a reference the president of a local bank located on the other side of town.
When the potential investors went to that bank to check out the reference, they found a busy, well equipped, and well furnished bank, full of well dressed obviously upper class clients conducting business. When they spoke to the President and other officers all they heard was praise for the honesty and business skills of the con man. The marks would then make a large investment.
When the con man left town with their money and they realized something was wrong, and then went to the bank to try to find out what was going on, they found an empty building with a "for lease" sign, and many of the people they had seen as customers and employees in the bank were now seen to be beggars, prostitutes, and such from the neighborhood that the con man had hired to play customers and employees.