I would go further and say never buy an old bike that you havn't seen in person and taken for a quick spin. The average digicam shot on an internet auction site is only going to tell you if both wheels are still attached and the paint is still shiny. It is not going to tell you that both the wheels are warped, the gear shifters are rusted solid, the bottom bracket is making a loud grinding noise and the headset is slopping around. Even an experienced mechanic isn't going to spot this in a poor quality photo. But even an inexperienced dummy is going to realise something is wrong within 2 seconds of jumping on the bike.