Had this problem a few years ago,brought an escort cosworth from a dealer in kent and I live in birmingham.Driving it back it was clear that most things on it were not right.I drove it home and was abit panicked,so set off the next day bright and early to take the car back, phoned in work to pull a sickey and phoned my soliciter on the way down there.
She told me the only way you can take something back was if you were sold something in which you thought you were buying something else,ie.honda civic type r prem addition and it turns out not to be a prem addition but as for the big end bearings you should have checked that all was fine and the seller will just say it was down to u,u checked the car over.