Is it legal for our offices to be checked by law enforcement?

Private investigator? Or can you check it yourself? If you call the cops, they will press charges if they find anything. Go the private route.

You have a Constitutional right to be free from an unlawful search and seizure. The police cannot search without a warrant. However, if they get a warrant you have to allow them to search what the warrant allows them to search (but nothing more). The police can always ask permission to search whatever they want to search. If you give them permission to search then they don't need a warrant as you have given up your expectation to privacy. If you have been contacted by the police you need to hire a lawyer. Don't try and make deals by yourself with a police officer. A police officer does not have any authority to make deals with you, and any promises he makes cannot help you later. Good luck and hire a lawyer ASAP.