In purchasing a guitar there are specific questions one should ask the seller to insure that the guitar you are hoping to purchase is free from any defects and is in proper working condition if it is an electric guitar. Also you should be asking questions as an inspection process for the seller ,who may not have working knowledge of guitars. This is both helpful to the seller of an item and to you as a purchaser. the first question as a buyer that you should ask in purchasing an acoustic guitar is the neck straight , this can be determined by the seller by placing the body of the guitar on the floor and holding the headstock and sighting down the neck. This will show any bows or twists in the neck. A bow if not to pronounced is acceptable as to you or a luither adjusting the truss rod to compensate for either a back bow or a front bow. An additional picture could be requested to determine how severe the bow is. The second question should be ,is ther any damage to the guitar.Then if no damage is inspected ask if ANY repairs have ever been made to the guitar, repairs can be  a neckset, a refretting ,a new bridge, new nut or a new saddle, some of these repairs are not harmful to the guitar,but some can detract from the value espically if it is a vintage guitar, In which you want almost no work at  all in the way of either repairs or work done to the instrument. A visual inspection for repairs can be accomplished buy the seller by loosening the strings and taking a small extendable mirror and a small flashlight and looking inside the cavity of the guitar for ANY extra bracing, any extra small cleats of wood along seams, broken braces, extra wood around the underside of the soundhole,and any cracks that may not show through the top of the finish on the outer side of the guitar. Always ask for extra pictures on any thing you want to see or on any questionable repair work.A good seller will; be happy to do this , if your questions are not answered or if you cant get the answers you want then the guitar in question might not be the one you want. I hope you find this guitar buying guide helpful while on ebay. www.gregsguitars.net  Thank you.