Lets say to agree to buy a mates cars for £1000. Done deal, just want to get an MOT done to check it's all okay.
The car needs a bit of work and your mate is a bit short, so you give him £400 for repairs, knowing the car is coming, and you will just need to give him the remaining £600 when the car is ready. You arrange an MOT that you pay for.
Meanwhile, your mate starts talking to someone else. Bit of a dodgy character. You find out he is arranging to sell the car to him. Apart from still wanting the car (well you paid for the MOT and a few repairs), you are worried you won't see your £400 again. Your mate doesn't have anything else to sell, he has no cash, once the car is gone, that's it. He might give you your money back once he sells the car, but this isn't guaranteed. That's not even the reason you leant him the cash - you were getting a car.
One thing you could do, is raise a court document that may prevent your mate from selling the car to this other bloke. Once this is in place, the court looks to protect you and the money you are owed, and stops your mate selling the car to someone else.
Also, it means you stand a good chance of getting your £400 back. It's a lot of money to you, why should you just lose it? You loved the car, but you'd rather get your money back than see some other guy driving around in your car that you invested loads of money in.
None of this means the car is going to be scrapped - it just seems fair and reasonable so that you either get the car you were promised, or you get your money back.
Hope that helps!
Disclaimer: This is just a way of explaining the situation from a single point of view. We are not privilege to any agreements or terms of any loans or payments, nor do we claim this to be accurate.