Don't buy product simply referred by retailer in place of other branded products you have chosen.

Sometimes we go shopping to purchase some predetermined brand item which may be the higher price compared to other product of same use and type. But have you ever noticed? You may be offered other brand item by the retailers/whole sellers in place of your preferred brand. And shopkeeper may try to lure you by explaining that the item offered by him is of superior quality compared to the product of particular brand you have demanded.

Is shopkeeper always correct in his approach? 

Answer is definitely "NO"

If the answer is no then why do they do this? What might be the reason?

They may do this for some benefits they get.

Let us elaborate this.

Branded products sales itself and doesn't require too much effort to make sales. But those products which sales itself or require no more effort to make the sale and allows low-profit margin to the retailers/whole sellers. And we all know business is done to earn the profit. And those products of the same type which are not of high brand value allows high-profit margin to the retailers/whole sellers. And thus retailers/whole sellers try to sell those items in which they earn high profit.

Thus whenever retailer/whole sellers try to sell you the product of other brand explaining that this product is better then what you were searching for them, don't believe him/her blindly.

Thus take decision wisely without biases of retailer/whole sellers and save yourself from the greedy retailer/whole sellers.