<em>I'm not from a business background so maybe some of the expressions you use are correct, but I'm not familiar with them. So my correction is based on standard English usage.</em>

The Influence of Advertisements (1)

(This is an IELTS writing test practice.)

Advertising plays a very big1* and important part in retail business. People virtually decide which consumer goods to buy by2* advertisements. There is a saying3* that the high sales of popular goods indicate the influence of advertisements instead of4* the true needs of the society.

Advertisements create lots of "wants", but not "needs". For example, few people really need Coca Cola or Pepsi Cola, but the selling records 5* of these two drinks are amazing. Spectacular advertisements should take most of the credits. That is why the advertisement advertising departments are one of the most important departments of these companies. They hire stars to perform in their advertisements every year. They are selling their advertisements, not drinks. People are buying paying for6* the advertisements, not the cola.

1* plays a very large part -sounds better to me. I think it is a collocation.

2* 'by' is correct but because it is the central argument of the text I would emphasise it with a stronger expression :

eg: People virtually decide which consumer goods to buy according to which advertisements they have seen.

or

People virtually decide which consumer goods to buy as a result of the influence of the advertisements they have seen.

3* I don't thing this is a 'saying' like an 'idiom'. I would use 'It is said that...'

4* I wold prefer 'rather than'

5* 'selling records' isn't an expression I know. I would have just used 'sales'.

6* The meaning is different, as what the customers take home is the Cola, not the advertisement.