Audio problem: In the Italian dub, Chief Sterns reads Mr. Pennington's number as 555-5219 instead of 555-5214. (00:28:30)
Audio problem: While Casey fends off the Foot Clan in the antiques shop, an answering machine falls from April's apartment above, hanging by its power cord. Charles' voice can be heard on the speaker, but after the cord snaps his voice can still be heard finishing a sentence. (00:46:50)
Audio problem: At the climax of the film when the Turtles are about to face Shredder for the first time, Raphael says, "I got him" and then runs to fight. When Raphael falls to the ground, his pair of Sai hit the ground but make no noise. There should be a metallic sound against the rooftop. (01:19:00)
Audio problem: In a close shot of Splinter holding Shredder's spear with Michelangelo's nunchaku on the building's ledge, Splinter's voice can be heard, but his mouth isn't even open (full screen version). (01:22:55)
Answer: It's not really petty thievery. Shredder essentially has control over a large crime syndicate which is involved in pickpocketing, burglary, and highjacking. And that's just the gang itself. The Foot Clan itself is probably involved with other activities that we haven't seen.