Bloomgarden v. Coyer, 156 U.S. App.D.C. 109, 116, 479 F.2d 201, 208 (1973) (footnote omitted) (adopted in H.G. Smithy Co. v. Washington Medical Center, 374 A.2d 891, 893 (D.C. 1977); see also TVL Associates v. A M Construction Corp., 474 A.2d 156, 159 (D.C. 1984). When, however, there is an applicable presumption that the services were rendered gratuitously — as occurs, for example, in the context of a parent-child relationship, see Tuohy v. Trail, 19 App. D.C. 79 (1901) — a promise to pay obviously cannot be implied by the mere rendition and acceptance of valuable services. The presumption itself, as a matter of law, negates any implication that "it would be unjust for the recipient to retain the benefit conferred" without paying for it. H.G. Smithy Co., 374 A.2d at 895; see also Farrin v. Harlow, 62 App.D.C. 314, 67 F.2d 580 (1933) (where plaintiffs rendered nursing services for eleven years to decedent, to whom they were not related but with whom they lived as a family, court, without explicitly invoking presumption, concluded services were gratuitous, not contractual). It follows, then, that when a presumption of gratuity is applicable — as the trial court held in this case — a claimant may only recover, if at all, by rebutting that presumption with evidence of an express contract or a contract implied in fact. B.