Who owns the trash? Let's say I invented a machine which turns trash into money. Can I legally: Take the trash from a trash deposit container outside my neighbor's house, without asking permission? Go to the landfill, load some trash into my truck, then drive away?
I'll assume a real question here and not one about a fan film on YouTube. Take the trash from a trash deposit container outside my neighbor's house, without asking permission? All depends on the locality; and sometimes the law is not settled, either. Some cities have passed laws that deem trash to be city's property as soon as it is placed in a city-supplied trash bin, because the city (or a private contractor) hauls to and owns the landfill. Other cities claim legal ownership of recyclables when placed on the curb, for the obvious reason that they are worth money. The law can be not settled if objects are in alleys and not in trash bins, or simply placed on the curb. For the sake of discussion, there are numerous examples of cities looking the other way with scavengers and pickers; it all depends on the location and the enforcement. (And, there are examples of the police being able to legally pull evidence from trash; but that's not the question here.) Go to the landfill, load some trash into my truck, then drive away? Think about it: you're obviously not going to be able to do this in a location with a managed landfill with employees that check you in and take your tipping fee. If it's a private trash contractor, it's private property; for a city, it's probably against the contract you signed when you paid to dump and probably against city law to salvage from the landfill, for liability reasons. (That doesn't mean the employees at the landfill can't salvage themselves; that's up to them.) But like anything, at an unmanaged landfill in a rural area, you could probably get away with it.
The pawn shop has the "use of property" of their own premises. The pawn shop has obviously the right to examine the gun to determine its value, for example, or to clean it if it needs cleaning to avoid damage, or to show it to a potential customer. And the pawn shop is allowed to let the police onto their own premises, even without a search warrant.
No. Theft is, in most jurisdiction, an action by which the offender takes another person's property with the intent to permanently deprive them of it. The clerk isn't taking any property from the store, and she doesn't have any intent to deprive the store of anything. She is therefore not guilty of theft. If she were doing this intentionally -- either in league with the customer or even without the customer knowing -- she could likely be held liable for the theft, either on a conspiracy theory or perhaps an innocent-agency theory. The lack of criminal liability of course does not mean that there can be no accountability. The employer is free to terminate the employee, and it will have different options -- depending on jurisdiction -- to recover the value of the uncharged printers, perhaps by docking her paycheck or through a negligence action.
It is their property, so keeping it without permission could well be seen as theft. I think you are obliged to make reasonable attempts to notify them you have their property before using it or selling it. Just like if someone left the item at your house after a party. If they want it back, however, it is at their cost, you should not be out of pocket for their failure to deliver within a reasonable time-frame; you may find they've already claimed the cost of the product from the courier and don't want it back. You are well within your rights to offer to buy it from them, and them to accept or reject that offer, this is a separate contract to the original sale.
In theory its only a crime if you know, or reasonably suspect, that it is stolen. The fact that you have to ask means that you have some level of suspicion, so that's not good to start with. In practice merely being investgated by the police will bring you a world of hurt long before it gets to trial. How much can you afford to spend on legal fees, and will you be able to make bail?
In the US it is generally illegal for you to open somebody else's mailbox. Your best course of action is to contact your neighbor and let them retrieve the package for you. In practice it might depend on your relationship with your neighbor. If you are good friends, they are unlikely to object or report you to the authorities as they'll be willing to trust that you were just retrieving your mis-delivered package. If you don't know your neighbor, or if you are on poor terms with them, they have no reason to trust your motives and they could reasonably think you were stealing from them or invading their privacy. As a tangential footnote: yes, people really can face federal charges for tampering with mailboxes. Recently a former city prosecutor and a former police chief for Honolulu were convicted of attempting to frame a relative on federal charges for stealing a mail box. A mistrial was declared on the mailbox theft charges, and in the process, an extensive web of corruption was revealed involving the former prosecutor and former police chief.
user662852 has a good point -- whoever own the property has the right to make the rules. Is the property, land+construction in fact your's or does it belong to the HOA who just grant you access as a lease holder? Different states has different rules, but in my state it is illegal to maroon a property and there must be a access to public streets even when this necessitate passing over somebody else land. However that is irrelevant if the HOA owns the land your house is build on. I think you will have to look at your HOA agreement and see what it says.
You have to give them back You don’t own other peoples stuff just because it’s on your property. However, you may be entitled to salvage rights - that is, payment for recovery of the vessel.