Casting Director's Conflict of Interest

Can a casting director or talent agent have a "conflict of interest" when they ask their actors to go out and buy products from a store to audition for that store's commercials?

I suppose casting directors and agents aren't holding a gun to actor's head telling them they must buy or else, but they sure are waving a carrot.

As actors, our agents make money when we book jobs. And casting directors make money when they are hired to find actors that will book the jobs... 
But why bring buying merchandise into the equation? Is the store that is making the commercial looking for another way to bring in revenue? By having thousands of actors across the country go into their store to buy stuff for the audition? Seems far fetched... yet it seems to be happening. defines a conflict of interest as: 
"The circumstance of a person who finds that one of his or her activities, interests, etc., can be advanced only at the expense of another of them." 

I am very curious what thoughts fellow actors, agents, and even casting directors have on this.

On the topic of "Conflict of Interest" I like Dan Ariely's talk & warnings.

Another side note, I am not certain on the actor unions stance on such practice? Do any SAG or AFTRA actors out there know?