Occupations that involve money are distasteful to the samurai caste. They are not inherently dishonorable, of course, for it is absolutely necessary for a samurai to oversee such activities to ensure that his Clan and family are adequately provided for, but it is definitely considered something of a social stigma to deal in commerce. The actual day to day trading and conducting of business is typically left to merchant vassals, but it is not unheard of for samurai to have training in such matters. These individuals are typically referred to as "merchant patrons."
The Appraisal Emphasis allows you to quickly determine the approximate value of an object in any given market. The value will vary depending upon the quality of the object's construction, how exotic or unusual it is, and how practically it can be put to use. More exotic or rare objects are not only more expensive, but also are significantly more difficult to appraise properly. The Mathematics Emphasis is typically used to calculate things like taxes and tariffs, but can obviously be used in a number of non-business applications as well.
Note: Mastery Abilites rank 3 and 7 are house rules and are not part of the standard 4th edition ruleset.