I placed a pallet in my garage to store some household items on and I have my garage cooled with a duct from my central air. I'm scared that any dirt from the pallet might get re-circulated through the central air vents in the house so I want to clean this pallet real good. Any thoughts or ideas?
It's still store property, and taking them without permission is theft. So yes, it is illegal. Even trash in a dumpster on their property is still theirs.
Yes, actually it is. That is theft. Most stores will let you have them - just go ask the manager on duty if you can take one. Once you have permission, there is no crime.
It is illegal to take anything that doesn't belong to you. Ask the store if you can have them before taking.
it could be some stores have a contract to have them picked up and recycled
Yes of course it is. They have to pay for those, they only get their money back if they return the pallets. They are not trash, they are private property that is used over and over again.