It all depends on the card. A lot of it comes down to how frequently a card comes up for sale and how in demand the card is when it comes up for sale. There are lots of rare 90s inserts that don't come up for sale that often and when they do people are willing to pay significantly more than book value. Then there are the dime a dozen cards that aren't that popular or rare and they can be bought for 10% of less of book value. So it isn't really cut and dry about a strict percentage of book value.
20 years ago things were very different, as the internet was in its infancy and people were still buying/selling the majority of cards at shops and shows. Back than there were pretty common percentages that were being paid (dealers would pay 25-50% of book value for a card and sell it for 50-100% of book value). With eBay, COMC, and other online storefronts the book values in Beckett aren't always inline with actual sales prices, thus the strict percentage rule has been lost.
20 years ago things were very different, as the internet was in its infancy and people were still buying/selling the majority of cards at shops and shows. Back than there were pretty common percentages that were being paid (dealers would pay 25-50% of book value for a card and sell it for 50-100% of book value). With eBay, COMC, and other online storefronts the book values in Beckett aren't always inline with actual sales prices, thus the strict percentage rule has been lost.
Collecting John Stockton, Karl Malone, Ivan Rodriguez, Gary Carter & UF player rookie year cards. Plus Jedd Gyorko rookie and prospect cards.
Jedd Gyorko 2010-2013: Have 329/419 including 1/1s
Wantlist: http://sites.google.com/site/sportscardsite/set-needs/
Jedd Gyorko 2010-2013: Have 329/419 including 1/1s
Wantlist: http://sites.google.com/site/sportscardsite/set-needs/