"The tailor is at the store."
Translation:Der Schneider ist im Laden.
"Say "bei" in combination with an indefinite article, if you refer to a company or instituion (bei einer Bank, bei einer Aktingesellschaft etc.) or in combination with an definite or without an article, if you refer to a particular company or instituion (bei der Post, bei der Bahn, bei der Technik GmbH, bei Müller & Söhne etc.)"
As far as I'm aware, many last names were derived from the bearer's profession and only later passed on to the next generations. Hence, there are a lot of last names in German that also are or were occupations.
Edit: look what I've found, a list with the most common names – and their original occupational meaning: http://en.wikipedia.org/wiki/List_of_the_most_common_surnames_in_Europe#Germany
The according German article states No. 1-15 were professions and that they predominate for the above mentioned reason. There are many more later on.