Deposit paid but failed MOT

System

It is common within the motor trade to not MOT a car until it has sold, it saves the dealer having a car sat there with the MOT ticking down and most people want a car with a full new MOT from a dealer.

Given it has failed on brake pipe corrosion I'm assuming an older car so even if it had passed a MOT with a clean sheet that is no guarantee there won't be problems in the future as the MOT only checks a small selection of things to do with safety and emissions. It doesn't for example tell you the condition of the cambelt, the clutch and things can pass a MOT and then fail before the next test.

If you want a guarantee of no problems you buy a new car but even then those come with manufacturer's guarantees because it is impossible to guarantee being able to manufacture a complex mechanical and electrical device that will be fault free for 3 or more years.