Question: a is an agreement by two or more sellers to refuse to deal with a particular person or firm

title: English contract law
text: When a contract is formed , good consideration is needed , and so a gratuitous promise is not binding . That said , while consideration must be of sufficient value in the law 's eyes , it need not reflect an adequate price . Proverbially , one may sell a house for as little as a peppercorn , even if the seller `` does not like pepper and will throw away the corn . '' This means the courts do not generally enquire into the fairness of the exchange , unless there is statutory regulation or ( in specific contexts such as for consumers , employment , or tenancies ) there are two parties of unequal bargaining power . Another difficulty is that consideration for a deal was said not to exist if the thing given was an act done before the promise , such as promising to pay off a loan for money already used to educate a girl . In this situation the courts have long shown themselves willing to hold that the thing done was implicitly relying on the expectation of a reward . More significant problems arise where parties to a contract wish to vary its terms . The old rule , predating the development of the protections in the law of economic duress , was that if one side merely promises to perform a duty which she had already undertaken in return for a higher price , there is no contract . However , in the leading case of Williams v Roffey Bros & Nicholls ( Contractors ) Ltd , the Court of Appeal held that it would be more ready to construe someone performing essentially what they were bound to do before as giving consideration for the new deal if they conferred a `` practical benefit '' on the other side . So , when Williams , a carpenter , was promised by Roffey Bros , the builders , more money to complete work on time , it was held that because Roffey Bros would avoid having to pay a penalty clause for late completion of its own contract , would potentially avoid the expense of litigation and had a slightly more sensible mechanism for payments , these were enough . Speaking of consideration , Russell LJ stated that , `` courts nowadays should be more ready to find its existence ... where the bargaining powers are not unequal and where the finding of consideration reflects the true intention of the parties . '' In other words , in the context of contractual variations , the definition of consideration has been watered down . However , in one situation the `` practical benefit '' analysis can not be invoked , namely where the agreed variation is to reduce debt repayments . In Foakes v Beer , the House of Lords held that even though Mrs Beer promised Mr Foakes he could pay back £ 2090 19 s by instalment and without interest , she could subsequently change her mind and demand the whole sum . Despite Lord Blackburn registering a note of dissent in that case and other doubts , the Court of Appeal held in Re Selectmove Ltd , that it was bound by the precedent of the Lords and could not deploy the `` practical benefit '' reasoning of Williams for any debt repayment cases .