Continuity mistake: When Brass and Grissom first enter the house of Ken Willard (the guy in the Polaroid), and Greg makes a noise at the door, the two of them turn around to see him. Then the angle changes, and they turn around again, repeating motion.
Continuity mistake: When Grissom, Brass, and Greg go to the house of the guy in the Polaroid, Brass picks up a credit card from a table. First, he is holding it by his middle finger and thumb from the back, then the shot changes to a close-up and he is holding it with his index finger and thumb along the sides. Then, we return to the previous angle and he is once again holding it with his middle finger and thumb from the back.
Answer: He doesn't have the authority to arrest him - when anyone is arrested in the show, a police officer does it. Also he tells Ty that he is going to be submitting his case findings to Ty's insurance company, who would no doubt contact the IRS, who then would have him arrested for fraud etc.