Case: The defendant (=def) wanted to do major renovations in her home and asked the plaintiff (=pl), a contractor, for an estimate. After presenting a detailed price estimate, pl was chosen and began working; def never signed the estimate. During the course of the work, many changes were made to the original plan, without additional estimates being made. There is now a dispute over payment. Def feels that pl overcharged for many of the elements of the job and that she should not be bound by charges to which she never agreed. She feels this is true not only regarding the changes but even regarding some of the originally stated prices. She explains that this is why she did not sign the estimate. Pl says that not only is def bound by his price estimates, but since he can prove that the prices for the new elements of the job are his standard prices, she is bound by them since she did not ask for a new estimate. Additionally, some of the new elements were just additional units of work included in the original estimate.

Ruling: Most monetary agreements require a kinyan (act of finalization). However, in regard to work obligations, the beginning of the work serves as the kinyan. In the case of work that is paid by the job, beginning the job obligates the worker to finish the job and obligates the employer to continue the employment until work’s end according to the conditions that were set (see Nimukei Yosef, Rif’s pages to Bava Metzia 46b and K’tzot Hachoshen 332:6). The fact that pl presented a work estimate and started to work should ostensibly mean that he is entitled to the stated amount.
On the other hand, def claims that the fact that she did not sign the estimate is an indication that she never intended to agree to those prices. The Shulchan Aruch and Rama (Choshen Mishpat 81:7) discuss the idea of shtika k’hoda’ah (silence can sometimes be understood as agreement). One application is that when a third party sets a price for a teacher to teach a child in the presence of the father who stands by quietly, the father is responsible (ibid. 336:1).
This concept certainly applies in our case. Def asked for an estimate and then without arguing over it, asked pl to begin working. This is equivalent to explicitly agreeing to the price. If she did not agree to the price, she should have told him before he began working. We should add that there is no common practice to wait for a signed estimate before beginning work. Therefore, the fact that def did not sign the estimate is not a sign of anything out of the ordinary. Even if we accept def’s claim that she had in mind to not bind herself to the price, "matters known only to the heart are of no consequence."