Stupidity: Why did the bad guys even go for Xander as he was snowboarding down the mountainside? First of all, it was impossible for them to even get to him as the mountainside had several cliffs. Secondly, why did so many go? Wouldn't it be clever to have as few as possible leave in case his snowboarding was simply to draw attention away from an ambush? They knew he was an agent by now and should know he could have gotten reinforcements. Thirdly, they could just have simply waited for him to get to them.
Stupidity: At the start, when the bank robbers pile into the car, Frank flips a switch and the licence plate changes...out in full view of the public. Given how well-prepared Frank is demonstrated to be, that's absolutely something he would have done in private, before arriving at the bank.
Suggested correction: The plate is changed after the robbery for a reason. By allowing plate A to be seen during the robbery the information will be relayed to the police that a car with registration plate A is involved. Swapping to plate B after the robbery ensures that police will see plate B and know that the car is not involved.
But the point is he drives up to the bank with plate A on display. The robbers pile in and he switches to plate B. So any witnesses have seen both plates (plus the fact that the car switched plates, doubly suspicious). Whereas if he'd switched to plate B while out of view in the car park, he'd still have a "clean" plate to use.