לרפואת משה בן מלכה בתוך שח"י
At the top of Kiddushin 66a we see that there is a difference between בעלים and עד אחד. Even if the בעלים are believed, that doesn't mean that an עד אחד is believed.
שורך נרבע והלה שותק נאמן ותנא תונא ושנעבדה בו עבירה ושהמית על פי עד אחד או ע"פ הבעלים נאמן האי ע"פ עד אחד היכי דמי אי דקא מודו בעלים היינו ע"פ הבעלים אלא לאו דשתיק
Your ox was used by a man for an act of bestiality and is therefore unfit for an offering, and the other, the owner of the ox, is silent, the witness is deemed credible. And the tanna of the mishna also taught (Bekhorot 41a): And with regard to an animal that was used for a transgression or that killed, if this is attested to by one witness or by the owner, he is deemed credible. The Gemara clarifies this case: What are the circumstances of this case of the mishna, where the knowledge is established by one witness? If the owner admits to the claim, this is the same as: By the owner. Rather, is it not referring to a case where the owner remains silent?
The Gemara tries to prove the נאמנות of עד אחד and the fact that the בעלים are believed is not enough. We see that בעלים have more נאמנות than an עד אחד.
If so, how do we understand Rashi [Yevamos 88a ד"ה אמר] who explains that we know עד אחד נאמן באיסורים b/c otherwise how could you eat at your friend's home? Yes - but your friend at his home is בעלים - not merely an עד אחד??!!!
