[rahimnathwani]

"I think its impossible to prove that any given $1 of advertising earns back $1 in profit for any sufficiently complex advertiser."

Even if that is true, that doesn't mean it's impossible to prove that your total advertising budget of $X improves your profit by more than $X.

[TeMPOraL]

It may be possible, but it's a hard problem. Are the people doing this calculation in your company competent in statistics, or are they just trusting what their ad management tools tell them?