I saw some auto knives for sale and the seller was requiring a copy of police of military ID in order to sell them.  I thought auto knives were only illegal in certain states like the PRK (where everything is illegal).  Or is it Federal law making them illegal everywhere?

Here in Oregon, it is perfectly legal to own, buy, or sell them. Just about every gun and knife store carries a complete selection of them.

It's legal to own ANY switchblade in California, and it's legal to drive to Oregon, buy one, and bring it into California as long as you put it in the trunk of your car.

You just can't carry them in public, sell them, give them away, etc.

From the California Penal Code:

653k.  Every person who possesses in the passenger's or driver's
area of any motor vehicle in any public place or place open to the
public, carries upon his or her person, and every person who sells,
offers for sale, exposes for sale, loans, transfers, or gives to any
other person a switchblade knife having a blade two or more inches in
length is guilty of a misdemeanor.

IOW you can make your own switchblade or keep one in your home, but you can't take it anywhere with you (unless you are an LEO, in which case they make good "throwaway" knives for those special situations).

Though it is illegal to import a switchblade into the US, they are one of the more popular items sold to tourists in Tijuana.  A lot of people have been busted for them, not realizing that they could face a federal felony charge.  Two women I know were once detained in secondary inspection and given body cavity searches because a Border Patrol agent found what he believed to be a switchblade in one woman's purse.  He regaled them with how they should have tried to smuggle a gun instead, because that would be a misdemeanor.  All the while the owner of the item kept saying "It's a comb", but they ignored her.  Finally one BP agent pushed the button on the item and out popped a comb.

That's when they REALLY got mad.  Border Patrol agents have no sense of humor at all.

Even where states have bans in effect some have exceptions for hunting, LEO's or if you have lost the use of or only have one hand.