In this case the search and seizure was not in violation of the fourth amendment. The fourth amendment is triggered when there is a search and seizure by the government which typically means the any government agent. But this does not apply to nosey neighbors who look through your home. A thing is searched when there is a trespass to person, houses, paper. The amendment come in to play when the government intrudes upon a persons property. Once triggered the four amendment requires reasonableness. A search or seizure must be reasonable for it to be constitutional. What make it reasonable is if there is a warrant or there is an exception.  For a warrant to be issued it need to be based on probable cause issued by neutral and detached magistrate and described with particularity.
If the dumpster was on private property rather than on commercial property It would have been different. Unless Agent Park had a warrant with probable reasons.

Bet-Air failed to identify its private property on the road leading to the dumpster containing the documents. In order for persons to preserve Fourth Amendment protection in the area immediately surrounding the residence, they must not conduct an activity or leave an object in the plain view of those outside the area. If the dumpster was on private property, with clear signage indications, Bet-Air would have the right to pursue legal action against the agent.  Clearly defined private property would provide transparency to the public.
As an executive at Bet-Air, I would ensure that there are proper measures in place to safeguard private property. Indicators such as signage, surveillance and fencing would be in place to limit public access to private property. This would maintain coordinated infrastructure and the “Fourth Amendment’s protection of business curtilage.” Ultimately, it would also avoid a possible unconstitutional search or seizure on the businesses premises.
 You mentioned the law of trespass.  Is this relevant as much now as it used to be?  How does this relate to the concept of curtilage?  What does curtilage mean?  How would this concept apply to businesses and to ones personal home?  Using this concept, how then would this apply to the Bet-Air case?