The concept behind shareware (or freeware) is that users deserve the chance to evaluate software before purchasing it. Applications of this type are generally available through the mail, from BBSs, or from FTP sites on the Internet. The recipient is on their honour to register the product for a set price if they continue to use it.
Sometimes the shareware version of an application is "crippled" in some way. Either it is limited in functionality, displays a registration notice periodically, or functions for only a limited period of time. Those who try the package thus have a strong reason to upgrade.
Many shareware aficionados view such tricks as being immoral. They prefer the carrot to the stick, and provide registered users with technical support, additional utilities, a printed manual, free upgrades to future versions, or other incentives. A rarer group of programmers do not request any money at all, believing instead in the benefits of sharing knowledge freely.
It is important to read the license agreement of a shareware package closely, as these vary widely.