Returning a discontinued kit would have done little for you anyway, maybe a refund.

Be careful buying used radios (anything really). Give it a careful going over, especially the batteries. Cycle them a couple of times if you can. New 4 ch radios are so cheap these days it just doesn't pay to buy used hardly. You can charge it up and do a range check without installing too and see how it is working. Don't have the transmitter on for a long time with the ant down though, not good for the output circuitry. 5-10 min shouldn't hurt. When you get around to doing the airplane installation just extend the ant. Sometimes the servos will "jitter" if the transmitter is too close, just move it away a few feet