Overview
A tout is any person who solicits business or employment in a persistent and annoying manner (generally equivalent to a solicitor or barker in American English, or a spruiker in Australian English).
An example would be a person who frequents heavily touristed areas and presents himself as a tour guide (particularly towards those who do not speak the local language) but operates on behalf of local bars, restaurants, or hotels, being paid to direct tourists towards certain establishments.
Types
In London, the term "taxi touts" refers to a kind of illegal taxicab operation which involves taxi drivers (or their operator) attracting potential passengers by illegal means—for instance, calling out travellers, or fetching them and their luggage, while parked in an area where taxi drivers must wait in their vehicle. They may charge exorbitant fees upon arrival, possibly using threats to ensure payment.
"Ticket tout" is a British term for a scalper, someone who engages in ticket resale for more than the face value of the ticket. In recent years some British ticket touts have moved into Internet ticket fraud.
From Wikipedia (CC BY-SA 4.0).