You could say the contractor's recommendations are pulled from a hat, like how a raffle winner might be selected - the recommendation has no rational basis or support, and is seemingly random.
One could also say the contractor is talking out of their ass, which occurs when a person expounds upon a subject with seeming authority, although they don't actually know what they're talking about. Another common term for this is bullshitting.
A way to express the utter uselessness of the recommendation is to remark "that and fifty cents will buy you a cup of coffee". Assuming a cup of coffee costs 50 cents (although not genreally true these days), the suggestion carries no value whatsoever.