People in other industries don't provide their would-be clients with "spec work" for free. That would be asinine. So, why do office furniture dealers, interior designers and manufacturers continue to do it?
It's not a new question. Toronto agency Zulu Alpha Kilo really illustrates just how ludicrous it is—in the great video below, in which a guy approaches real men and women (not actors) in other businesses and asks them to provide him with a product or service for free, to see if he likes it before committing to more.