Brainyquote has many Twain quotes; many or most of them I know to be verifiable Twain quotes, but there are several I question, such as "Denial ain't just a river in Egypt," which can be seen here:
Are the quotes assembled there at brainyquote a combination of actual Twain quotes with apocryphal, albeit mostly Twainesque quotes? Or is it a trustworthy source.
 - B. Clay Shannon