As far as the Islamic Law is concerned, there is nothing wrong with trading a used car for a new one, as long as there is no deceit on either part and there is no unjust raising or lowering of the price by means of monopoly or exploitation of the weaker party.

Dr. Monzer Kahf, a prominent economist and an expert in Islamic finance stated that

‘trading a used car for a new one is permissible; the issue of price is subject to negotiation and consent. It is an issue that the sharia does not interfere with, except from the point of view of monopolistic power. It is haram to exercise a monopolistic power that ends up unjustly raising or lowering the price on the weak party, a buyer or a seller.

The hadith about date is correct, but there is no analogy between date and cars. Date is a cash crop that was a general staple food item at that time in Arabia. The rule applies to similar cash crops. On the other hand, we also have correct hadiths about exchanging one camel for two