a) The commercial law concept relevant to this scenario is "Implied Terms." Implied terms are terms that are not explicitly stated in a contract but are still considered binding between the parties based on the nature of the agreement, custom, or legislation.
b) The relevant law to consider in this scenario is the Sale of Goods Act 1985 (Revised Edition).
c) Quoting the relevant law:
Section 14(2) of the Sale of Goods Act 1985 states: "Where the seller sells goods in the course of a business, there is an implied term that the goods supplied under the contract are of satisfactory quality."
d) Applying the law to the scenario:
Based on the scenario, Mervin, as a seller, sold the car to you in the course of his business as a mechanic. Therefore, there is an implied term under the Sale of Goods Act 1985 that the goods (car) supplied should be of satisfactory quality.
In this case, Mervin carried out the repair works on the car engine himself without notifying you. As a result, the car was eventually destroyed in a fire in Mervin's garage. This indicates that the car was not of satisfactory quality, as it was not delivered in a safe and usable condition.
Since the car was destroyed and you are not insured, you have a valid claim for non-delivery and can demand your money back from Mervin based on the implied term of satisfactory quality under the Sale of Goods Act 1985.
Brief conclusion:
Based on the provisions of the Sale of Goods Act 1985, Mervin, as the seller, breached the implied term of satisfactory quality by failing to deliver the car in a safe and usable condition. Therefore, you have the right to demand a refund for the non-delivery of the car.
Please note that it is always advisable to consult with a legal professional for specific advice tailored to your situation.