Alien Raiders (2008)

This is a decent flick - except for the horrible title and obvious ending.  A small town supermarket is over run by a group of masked intruders in what initially appears to be a robbery.  The group rounds up employees and customers and appears to be searching for someone specific.  One of their team mentally scans people in the store, and those deemed okay are segregated from those who have not been checked.

An off duty police officer, who happens to be in the store, calls in to report the masked intruders.  The intruders exchange gunfire with the officer, who is hit.  The group's scanner is killed.

At this point, the group panics.  It turns out they are scientists who are trying to eliminate dangerous aliens among us and with their scanner dead, there is only one other way to tell who has been absorbed by aliens and it involves using a knife.

The police arrive with a hostage negotiator who turns out to be the father of one of the hostages, a young cashier.

While I enjoyed the film, the ending was really obvious. Plus there were some questions that went unanswered:

1. How did the scientists know that the alien would be at that supermarket at that particular time?  Wouldn't it be more likely that if it was definitely going to be there, you could concentrate on employees rather than customers?
2. How could a team who obviously had prior experience tracking and eliminating aliens, (based on all the videotapes of prior missions), not do a complete sweep of the building?  
3. Even if they believe they have the king, why let anyone else leave without scanning them?  They still might be infected and a second scanner has arrived.
4. When the teen cashier argues that she knows they will be killed and need to escape, why does anyone listen to her?  First, listening to her father's stories of hostage negotiation does not mean that she has the same knowledge.  Second since the intruders already let some people go there is no reason to think they won't let the others go.  Lastly, the scientists are obviously looking for someone specific rather than a random search, so if you have nothing to hide you should be okay.