Continuing on.
A best work gun will have 75% + coverage of high quality engraving, your first clue. The stock wood will be of high quality and usually well colored and figured - second clue. The stock will be shaped, checkered, and finished at a very high level of craftsmanship. Barrel striking and finish will be excellent. The action will also be well fit and finished. Unfortunately, there is no "short course" that will give you knowledge of all the above.
Questions to this point? More if anyone is interested.
DDA
I can't agree with the point above on engraving; It is not all that uncommon to find true BEST guns by the big names with either very basic, or even no engraving. The BEST relates to the materials and workmanship, not the addition of engraving. I would however agree that IF engraved, the engraving of a BEST gun should be BEST quality engraving (regardless of what design or type is used).