Answer: adverse selection
Step-by-step explanation:
Adverse selection is a situation whereby the sellers possesses information that the buyers do not have. It may also be the other way round whereby the buyers have information which the sellers don't have regarding the quality of a product.
There is information failure between both parties; typically, it's usually the sellers who has more information. Therefore, base on the scenario above, charging same rate or lower rate after the date of the purchase would expose ABC to adverse selection problems.