Conclusion of the argument : when the selling price is held constant, consumers tend to perceive offers with higher suggested reference prices as presenting a better deal

we need something that strengthens the above statement

A- Acquisition value does not affect consumers' assessment of transaction value.
>This cannot be assumed as per the first sentence of the argument. This neither strengthens not weakens the above conclusion

B- Advertised reference prices may differ from manufacturers' suggested retail prices.
>Try negating, Adv ref price will be same as Retail price, this dosent weakent the argument.

C- Consumers almost never pay the full advertised reference price for a product.
>Irreleavent point to discuss

D- Consumers perceive most suggested reference prices in retailers' advertising to be sufficiently credible as a guide to transaction value.
>Correct

E- Transaction value is more important than acquisition value in predicting consumer purchasing behavior.
>Argument never does the comparison between transaction value and acquisition value, it only says both are necessary