Graphic design is not liable for selling the product, the product is

Graphic Design mainly serves as a means to present an idea, product or message

And truth be told, there’s only so much that graphic design can do.

Let’s take a music concert as an example, regardless of how well-designed a poster might be, I won’t go see ‘artist this+that’ if I’m not into their music. And I’m likely to buy a ticket to any concert that has Andreas Vollenweider in its line up — regardless of how cheap, crappy or poorly design the concert’s poster and/or other marketing collaterals are designed.

In away, the best a poster can do in the above case, is to say “Hey, artist: this+that, is coming to town and they’ll be performing hits: this+that” and provide important information such as the date, time and ticket cost etc. — and that’s it!

Obviously, a poster that succeed in attracting attention means more consumption of whatever it is that you’re communicating or selling. But drawing attention to a poster is not only dependent on the poster (design) itself — where the poster is placed can do the job with ease, provided the poster contrast well with its background.
No amount of great design or a billion’s worth of a campaign can make me buy any brand of beer — as I drink, not.

And no amount of great packaging design will make me buy CorelDraw over Adobe illustrator — the product, software in this case does the talking in the company’s sales pitch. In cases like the above example (music concert),
Graphic design is the presentation of a sales pitch — not the sales pitch.