4Seventy is absolutely right about buying a used double rifle. If the road to Hell is paved with good intentions, the path to a good used double is even worse, if you don't know what you are looking out for. Most of us don't know!
Been there done that and bought the T-Shirt.

If you want a double rifle the best thing to do is be patience and seek the advice of someone who does know. If the person you are buying a used double rifle from won't let you have it checked out or shoot it as a precurser to your buying the rifle. You need to find another deal, or be prepared to fix the problems it might have!

Hard to believe, but there are those folks who will just like to take your money! The old saw about an ounce of prevention applies to being cautious when buying a used double.