Why did John and Lorraine go to Tony's Market in "The Pigman"?
John "drag(s)" Lorraine down to Tony's Market immediately after their first visit to the Pigman's house to cash the check the old man had given them.
John and Lorraine had contacted the Pigman as a prank. Once they got him on the phone, they posed as charity workers and asked for a donation. The Pigman, lonely for human contact, agreed to give them a check, which they arranged to pick up at his house. When John and Lorraine arrive at the house, the Pigman, Mr. Angelo Pignati, invites them in. Pathetically happy to have visitors, Mr. Pignati talks to them about a variety of subjects, and shows them a memory game and his collection of pig figurines. When John and Lorraine are about to leave, the Pigman gives them the check he has promised for their charity, made out, at John's direction, to cash.
The teenagers in the area frequent Tony's Market, because Tony "sells beer to anyone and for some reason the police leave him alone". Lorraine believes this is because "Tony has a nice, friendly face and believes in the old days when they thought a little alcohol was good for everyone...sort of a father-image with a cultural lag". Whatever the case, John knows that they will be able to cash Mr. Pignati's check there with no questions asked, and so he and Lorraine go straight to Tony's Market after leaving the Pigman's house (Chapter 5-6).