However, if either refuses to complete the bargain (either the prostitute after being paid or the payer after receiving the services), the court will not assist the disappointed party.
In Germany, where prostitution is also legal, a law exists that – once a contract has been entered into – makes a prostitute's demands for payment legally enforceable (even via collection agencies and courts if necessary), but the client's demands for fulfillment of the contract and rendition of sexual services would be unenforceable.
In many jurisdictions, racially or ethnically restrictive covenants excluding disfavored groups such as Blacks or Jews were common until the 1940s.
These were ruled unconstitutional in 1948 in the Shelley v. Kraemer case and therefore legally unenforceable.
A contract can be said unenforceable if it goes against the statutes of fraud or the Statement of Goods Act.