The following restrictions should be abide when registering a .BIZ domain name:

The .biz domain can only be used for a "bona fide business or commercial use".
A bona fide business use is one of the following:
   1. To exchange goods, services, or property of any kind;
   2. In the ordinary course of trade or business; or
   3. To facilitate
      (i) The exchange of goods, services, information, or property of any kind; or,
      (ii) The ordinary course of trade or business.

Registering a domain name solely for the purposes of:
   1) Selling, trading or leasing the domain name for compensation, or
   2) The unsolicited offering to sell, trade or lease the domain name for compensation
       Does not constitute a bona fide business or commercial use" of that domain name.

For illustration purposes, the following do not constitute a "bona fide business or commercial use"
of a domain name:
   1. Using or intending to use the domain name exclusively for personal, noncommercial purposes; or
   2. Using or intending to use the domain name exclusively for the expression of noncommercial ideas
      (i.e., registering Xsucks.biz exclusively to criticize or otherwise express an opinion on the products
      or services of X company, with no other intended business or commercial purpose).