Case:


Ruling: The gemara (Bava Batra 138b) says that beit din does not look into a matter that another beit din ruled on (see S’ma 19:2). However, since the first case was between pl and Reu and this one is between pl and def, it is not the problematic rehashing of the same claim. Also, the Chatam Sofer (Likutim 50) says that when the second beit din knows the basis of the first beit din’s ruling and disagrees, they can follow their own understanding. After receiving the reports of appraisers and interviewing Reu and other professionals, beit din concluded that even the estimate was exaggerated, not to mention the final price. On the other hand, pl knew that and did not argue with Reu. Although he hoped that def would lower Reu’s price, he did not say anything to Reu.
The Rama (Choshen Mishpat 129:2) says that if Levi falsely tells Yehuda that Shimon is safe to loan money to, which he then did and did not recover the money, Levi must pay because it is as if he became a cosigner. Similarly, the Rama (CM 14:5) says, regarding one who told his friend to go somewhere because the former would follow and he did not, that he has to pay expenses. The Gra (14:31) explains the latter halacha is based on garmi (payment for semi-direct damage). The Netivot Hamishpat (232:2) says that it is an implied self-obligation, along the lines of a cosigner.
One of the differences between the explanations is that garmi requires negligence, whereas a cosigner can be obligated by an honest mistake. In this case, the recommendation of Reu, a respectable professional, was not negligent. Regarding the price charged, if def said that he would see to the matter, there would be grounds to obligate him. On one hand, def denies this. On the other hand, from his response to questioning in beit din, it is unclear whether he accepted responsibility. Beit din cannot obligate him to pay, but there is room for pl to have taromet (grievances) against def, and it is proper for def to monetarily appease pl until he forgives the damage he was caused.