Well, you're an unknown newbie... 20€ beforehand, 280€ afterwards does indeed mean that the person taking your deal doesn't lose money, but it also means that the odds of you dissapearing and not paying the 280€ are great... No offence, but what would be your incentive to pay the 280€?

Maybe using an escrow would increase your chances of finding somebody to make the purchase?

By the way, i assume you want to buy something legal?