Finding out a customers occupation is crucial to insuring a customer. Commercial vehicles are usually used for business purposes, it is a key rating factor for insurers.
Common occupations for a van driver are usually trades people. See below the usual occupation's that come up-
Builder
Plumber
Carpenter
Electrician
Roofer
Painter and decorator
Tiler
Company Director
If the customer selects an occupation that is not allied trade, like listed above. Then it would be wise to probe why the customer has purchased van over a car.