New collector (and not a real smart one) would like to know.
Having come from a coin collecting background, I have always had an interest in paper money. When all we had were raw coins to buy, most collectors learned the hard way by getting burned buying cleaned/altered/improved coins.
I steered away from paper money collecting years ago when I learned that paper money was being improved/cleaned by washing, steaming and ironing (presumably to remove folds, wrinkles stains etc.). I've been buying graded currencies to avoid this pitfall, but, I really have not seen this issue addressed in the collecting community. Is this an issue when collecting paper money? Are there a lot of "raw" notes that have been altered to "improve" them and passed along? Inquiring minds would like to know...please comment.