Posted By:
petecldDan,
It's hard to offer an opinion without seeing the cards involved. You don't mention if it's a 1914 or a 1915 Cracker Jack. BIG difference in value. I've heard many people describe PRO graded cards as "looks great" so that doesn't really say anything. There is a 1914 CK Cobb on eBay right now.
You said, "...the seller is top notch and has been around for a number of years." Then why didn't he have it graded?
$700 for both B-18s - Cobb and Jackson - is a good price but ask yourself if it's "too" good a price. It's a lot of money to loose on cards you aren't familiar with.