The first thing I look for above anything else is to make sure the film has no vinegar smell. Vinegar means that the film is starting to break down, becoming brittle and useless eventually. This condition usually comes about by poor storage conditions. Too hot or too cold and moist are poison to films eventually. If the seller on ebay doesn't mention if it has smell or not, I always ask. Sometimes film can become brittle and not have the smell. There are various chemicals that you can buy that will make the film more plyable and lessen the chance of it breaking in your projector, but only if the film doesn't have 'vinegar syndrome'. I also look for film with a description of the contents from the original owners (usually notes with the film), or film that has been watched by the seller. If they say they have no projector and have not watched the films, you could end up with blank film or non-stop shots of someones baby learning how to walk. A film leader is important. Its usually plain white film that you use to thread the projector with. Unless the contents that the seller lists are excellent, I don't bid on film without a leader. I don't want to thread up my projector with the beginning of the acutal movie, because you miss something good at the beginning that way, and it could have a quick shot of Elvis at a county fair in the 1950's singing. Sometimes the seller will say where he bought the film. Film that comes from a big city or near a big city will probably have shots of that city. My main preferences is footage from cites near Disneyland or Hollywood, because some very good footage can be obtained that way. Even if the seller has not watched the films, I would buy these types of films anyway in hopes of finding some shots of anyone famous. Its kind of like playing the lotto. Always look for someone that will send the films media mail, because it will save you a fortune in postage.