The 1926 Sesquicentennial differed from the numerous commemorative issues of the 1930's in several ways. First, there is no doubt about the worthiness of the event commemorated, the 150th anniversary of American independence. Second, there were an enormous amount of Sesquis minted (1,000,528), but about 86% of the original mintage (859,048) were melted as unsold at the issue price of $1.00 per coin. Still, this made the Sesqui one of the highest "mintage", i.e. actually distributed to the public, of all silver commemoratives of the 1892-1954 classic era. Finally, though the mintage was very high, the design was poorly executed and very flat, thus most issues have lots or scraps and marks and Gem MS65 examples are rare. In this way the 1926 Sesqui is very similar to the also "flatly designed" 1923-S Monroe.
The typical Sesqui is MS63 or MS64. Because it was an "early" commemorative issue, i.e. struck before the flood of commemoratives issue during the commemorative collecting mania of the 1930's, Sesquis were not all saved and many reached circulation. Gem MS65s are rare and there are only about a dozen or so known Superb Gem MS66s. I personally have never seen or heard of a Sesqui that grades MS67 or higher. The big problem is scraps and marks, particularly on the face on the obverse. Sesquis come with varying degrees of toning, including a very unattractive yellow. The yellow coins sell for a considerable discount and it seems there is somewhat of a two tier market...decent eye appeal coins and yellow toned coins. Obviously, collectors prefer good eye appeal over ugly yellow toning!