jemandem etwas aufschwatzen
To chatter something onto someone. Duden: to talk someone into buying or accepting something. One of its examples is a magazine subscription bought at the front door from a sales representative.
jemandem etwas andrehen
To turn something onto someone. Duden: to talk someone into buying something, often something inferior or unnecessary. Its example is a vacuum cleaner.
der Klinkenputzer
The door-handle polisher. In its first meaning in Duden: a man who offers something for sale at the front door.
die Drückerkolonne
A gang of pushers. Duden defines a Drücker as a man who goes from door to door to sell something, especially magazine subscriptions. A Drückerkolonne is a crew of them. In 1998 the taz called the trade die organisierte Verantwortungslosigkeit, organized irresponsibility.
Es besteht kein Zwang, etwas zu kaufen.
There is no obligation to buy anything. Duden uses this sentence as its example for the word Zwang, compulsion.