Aside from knowing that Evan Marriott is actually a rich boy, male model and second-rate, bit part, soap actor (Days of Our Lives), I don't think anyone involved in the production is being deceived either. I think the other 20 girls know exactly what's going on. They all looked like second-rate actresses as well.
The whole thing smells scripted.
They harp and harp and harp on the fact that Evan is this ordinary construction worker guy making $19K. So much so, that I think it's to draw the attention away from something else.
It wouldn't surprise me, for example, that when he picks The One and starts telling her that he didn't inherit all this money, that she breaks it to him that she's actually an actress hired to play along (they all were), that she's married with 2.24 children and has no interest in him at all.