For applicants to be able to claim that they have relied on incorrect information in accordance with the principle of good faith, it has to be established that the erroneous information from the EPO was the direct cause of the action taken by the applicants and objectively justified their conduct (T 460/95 of 16 July 1996 date: 1996-07-16; G 2/97, OJ 1999, 123; J 5/02; J 5/07; J 10/17). According to J 27/92, it must be established that, on an objective basis, it was reasonable for the appellant to have been misled by the information. Whether or not this was the case would depend on the individual circumstances of each case.

In T 321/95 the board stated that the alleged oral agreement was not mentioned anywhere in the communications between the primary examiner and the appellant and was not derivable from the content of the file either. Thus, arguments supporting the allegation of a violation of good faith could only be considered as the appellant's personal opinion, which did not convince the board because there was no evidence that there had been any agreement in the sense mentioned by the appellant instead of simply a "miscommunication" between the primary examiner and the applicant.

In case T 343/95, dealing with the content of a telephone call on which the appellant based its allegation in respect of principle of good faith, the board was of the opinion that even if it was not possible to establish the call's content beyond any reasonable doubt a posteriori, in a case like the one in hand it was sufficient that the board was satisfied on the basis of a balance of probabilities (i.e. that one set of facts was more likely to be true than the other). In the case in hand the conditions for the application of the principle of legitimate expectations were fulfilled (but see T 188/97, where the board could not establish the facts surrounding a telephone conversation with sufficient certainty to invoke the principle of legitimate expectations).