Revealing mistake: When Warrick takes out the contents of the wallet, he removes a few 100 dollar bills. If you look carefully, you can see on the top bill it says "For Motion Picture Use Only."
Revealing mistake: Season 5 Episode 18 "Spark of Life": when they show a closeup of the badly-burned woman during her debridement, it can be seen that even though her eyebrows and hair and, in fact, 90% of her skin has been burned away, she still has long, full eyelashes.
Revealing mistake: Season 5 Episode 4X4. When Warrick and the young coroner are examining the dead woman in the RV, look closely as you can see her blink.
Revealing mistake: Willows discloses a laptop with the city's grid layout inside the welder's truck, and grabs her cell to call Grissom. Just as she presses last number, he immediately answers, without so much even a ring.
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.