This question is fairly simple. If one understands the meaning of the argument and identifies the main idea, it would not take him/her more than 30 seconds to answer this question. Hence, we will try to understand the argument.
There is a difference between something to be true and something 'perceived' to be true. 'Perceived' to be true are usually the cases that might or might not be true, but they are considered true.
According to the argument, an advertising agency said that:
> quality of the client's product is perceived to have decreased
> it so happened because the client had pressured the agency to create a campaign
> the campaign pressured by the client sacrificed the product's image
> the product's image was sacrificed to establish the product as a bargain
So basically, the author is trying to convey that by sacrificing the product's image to establish it as a bargain, the quality of the product is perceived to have decreased. For Quant fanatics, the argument seeks to establish that - (the perceived quality of the product) is indirectly proportional to (the perceived bargain of the product)
Now that we have understood the meaning, let's attack the answer choices and figure out which one of the following would weaken the argument the MOST-
A. A client will always switch advertising agencies when the perception of that client’s product’s value decreases.
> Doesn't matter. While it could be true that the client will always switch advertising agencies, it is out of scope in our context. Remember that something that might be true in the real world need not weaken the argument. Such answer choices are usually traps in difficult assumptions and weakening questions
B. The client has to give final approval for any advertising campaign an agency creates.
> This does not change our argument because the argument itself says that the client had pressurized the advertising agency, so indirectly it is pretty much true that the client provided the final approval
C. Perception of the quality of a product increases when the perception of that product as a bargain increases.
> Now we are talking! What we inferred from the argument is that (the perceived quality of the product) is indirectly proportional to (the perceived bargain of the product), i.e. the perceived quality of the product decreases when the product is perceived as a bargain. However, the answer choice says exactly the opposite. So if the answer choice is correct, then our inference is incorrect and the whole argument falls apart. Hence, this is correct answer choice
D. The perception of a product’s price value increases when an advertising campaign is successful.
> Success or failure is not in context here
E. It is impossible to establish a product as a bargain without a decrease in the perception of that product’s quality
> It flips the relationship between perception of quality of product and perception of bargain
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