As time goes by the supply of Mint condition collectibles continues to decrease while the supply of marginal condition items increases, assuming production of the item has ceased. As collectors become more experienced their demand for collectibles in excellent condition increases while items in poorer shape become less desirable. Many Beatle records, books and magazines were mass produced in the sixties. Abused vinyl, battered books and clipped magazines are today worth little more than their original purchase price. However those that have survived the past 30 years intact and in pristine condition are very rare and carry high price tags.
Some items are so scarce that they command high prices in almost any condition.
Knowing which items means doing your homework. Items manufactured recently are often produced in huge quantities. Initial demand may be high but is typically short lived. An example is the set of Beatles trading cards by the River Group. Although they are of high quality they were produced in massive quantities, enough to satisfy all interested collectors.