Unfortunately demand for detectives is very low and nobody will hire you as you have no experience and don't even know what detective work is.
Detective agencies do no only undertake work following cheating husbands or wives, although it is a common instructions. Private investigators also do a lot of work with companies who may have staffing issues whereby they may need corporate surveillance, computer forensics, handwriting analysis or pre employment screening. They also work with solicitors who may need legal documents personally serving or assistance on a specific ongoing case.
I don't think detective agencies exist. Sounds fun though.
It's one of those jobs that probably exist a lot more on TV and movies than in reality. The market for private policing and surveillance is pretty limited in the real world.
