Many letters will have folds or bends in them because of the mailing process so, as long as there are no major flaws such as tears or staining that affect the content, the value won't be affected very much. Content is another major factor. As a general rule, the more sports related content, the higher the value. Another content-related factor revolves around the amount handwriting found in the document. With all other things being equal, if a letter is handwritten, it is usually worth more than a letter that is typed.
Collectors seem to like the personal touch the handwritten pieces offer.
This guide should be used for non-game equipment. Autographed game issued or game used equipment would command a much higher premium than the prices listed in this guide. The autographed bat, glove, jersey and helmet prices listed are for replica or commemorative-type items. General condition principles apply. Flats - General condition principles apply to all other miscellaneous flat items.