ANSWER TO WHERE'S THE MONEY?

This is a sort of verbal card trick, where numbers are flashed about to distract you. There is in fact no missing £1000. As Pete Doughty put it:

"Quite confusing that one, took me a while!

If the 3 people give £10,000 to the Salesperson, but get £1,000 back, they have each spent £9,000. A total of £27,000. Given the car cost £25,000, the extra £2,000 is in the Salespersons pocket!

Basically, you have to ignore the £30,000. Assume the car cost £25,000, but they paid an extra £2,000 which has gone to the Salesperson."