These are basically the basic messages I gleamed from the pages of this book - I was so eager to jot them down somewhere, before returning the book to the library [edit: about 10 years ago].
I think Green passed away several years ago [and may have been more of a coin collecting enthusiast] and this book was published all the way back in 1994 - but it features some pretty good stuff if you are focused on the bottom line of trading cards, whatever that means these days.
1.) Go for the home run all the time.
2.) Be selective all the time.
3.) Avoid non/odd-sport cards.
4.) Buy established HOF bound stars.
5.) Avoid injury prone players.
6.) Avoid late bloomers - 24 and up.
7.) Avoid autographed cards and sell them off - presumably uncertified autograph cards.
8.) Avoid questionable players.
9.) Buy the real thing - not reprints.
10.) Avoid guys without championships.
11.) Avoid draft picks.
12.) Avoid two-sport stars.
13.) Avoid special cards - like leaders or all-star cards. Buy players' actual cards.
14.) Avoid non-glamour positions - offensive linemen in football.
15.) Avoid oddball and black and white cards.
16.) Avoid stars with `mediocre' years.
17.) Avoid players who shift positions.
18.) Look for players with five monster years.
19.) Beware of the hype or the stats - today's stars are destined to be commons.
20.) Avoid baseball players who would have to defy all historical trends to make Cooperstown - the Hall of Fame is all that matters.
21.) Avoid stars without a significant stat - 500 home runs, 300 wins, etc.
22.) Catchers get injured.
23.) Take advantage of people's nostaglia - money now or profit never.
24.) Cards that are priced too high will come down in price - no matter how scarce the cards, without demand prices drop.
25.) Do not worry about prices - price guides are guided by dealers.
26.) Condition matters.
27.) Ship cards to regional areas or donate cards - do not be greedy.
28.) Supply and demand - buy when prices are low and sell when they are high.
29.) Anticipate demand and potential decrease before it takes place.
30.) The goal is to sell close to retail value.
Blacklist Cards By Paul Green