but there's no reason to do it all at once. if you are trading 1 btc for money there should be an automated way to do the transfer in increasing steps, after each of which the other party would reply - so transfer 0.0001, 0.001, 0.01 etc. til you are done. You wouldn't lose much, and you could vary the rate depending on how much you trusted the other party.

But there's no reason to leave a quarter of a million dollars in BitCoins in an untrusted 3rd party's hands. Unless you're lazy or naive. It takes almost no effort to transfer them to your own wallet which can be trivially encrypted or stored on a device unconnected to the Internet.