If a cop in delaware...?

No, an officer can not search based on expired registration. The burden of proof required to do a vehicle search is probable cause.

You can refuse to consent to a search, but if the officer has a legal reason he will search anyway.

Was the officer allowed to search? As I mentioned, probable cause if required to search without consent. However, the officer is not required to tell you what the probable cause is. Without knowing what the officer was thinking, it is impossible to answer that.

Since none of us were there, it's difficult to know the exact circumstances regarding why the officer did what he did. If your father was issued a summons, and he feels that the officer should not have searched his vehicle, he can call the department and file a complaint against the officer. If the officer had run your father's license, he would've already known about the CCW (if you have one in the state you lice, and an officer runs your information, that detail comes back with the driver's information). But as the first answerer stated, you can refuse a search if the officer has no just cause to search the vehicle. If he smelled marijuana, he can search, but most times they are looking for someone who's transporting large amounts of drugs. If someone refuses to allow their vehicle to be searched, we might get more suspicious, but we can't force you to let us search.

Yes u can refuse a search. And the cop had to have reasonable doubt to why he searched the car. For example if your father looked high or if the car smelled like drugs then the cop has every right to search. But in this case it doesn't seem lik the cop had reasonable doubt. So if I were u I would tell ur dad to complain to the police department u never kno if the cop has done it before to other people. Good luck