There are two types of implied contracts.

Contracts implied in fact contain all the necessary elements (offer, acceptance, and consideration), except that these contracts are not in writing nor have their elements been stated orally.  They are inferred from the parties' conduct.  Contracts implied in law (aka quasi-contracts) are not even contracts.  They are equitable remedies imposed by courts to prevent unjust enrichment.  

Three elements must be shown to establish a quasi-contract: (1) the plaintiff (the business bringing the suit) conferred a benefit on the defendant, (2) the defendant was aware of the benefit, and (3) the defendant accepted the benefit under circumstances that made it inequitable for the plaintiff.  In addition to these three showings, a plaintiff must prove that one of the following is true: (a) the plaintiff had a reasonable expectation of payment, (b) the defendant should reasonably have expected to pay the plaintiff, and (c) society's reasonable expectations of security of person and property would be defeated by nonpayment.