פירוש על בבא מציעא 68:12

For he (the lander) may take out the collateral... Rashi explains that will make him (the borrower) disquilifed from testimony and from swearing, (if he is proven wrong after he swore).

this is difficult to Rabanu Tam, for is this is the reason (that the borrower may be proven wrong) would only encourage the borrower to be more precise when he swears, so he should not be able to be proven wrong, and why would we establish a rule to help a lier (by placing the pledge on the lander, so the borrower does not get caught lying). and if your concern is that possibly the borrower will swear in truth (about the collaterals value) and the lander will take out a ruined collateral and that would make it seam like the borrower lied). if so (that we are concerned about the collateral being ruined and decreasing in value) why does the Gemera suggest later on that the borrower can try and find the thief, if that wont prove he is right. (for we are concerned that their is a decrease in value). so if are concern is that it may be valued more then the borrower swears, this will only lead for him to be careful with his pledge?

so it seems to Rabanu Tam like Rabanu Channel for (if the lander takes out the collateral) it seems like the borrower swore for no reason. and its a disgrace to swear when its possible that we will find out the value when the lander takes it out, but if the lander will swear he will only do it once he is sure that the object wont be found.

on Rashi the children paid: (Rashi points out) and the father did not have chance to say he will pay, before he died (till here is rashi)... (Rashi) needs to explain (the sequance of events) in this way, for if father had said he will pay (before his passing), it would be simpel that they son get the rights to double. except in a case where they clerly backtracked (on their fathers words) and said they will not pay... however (says the Penei Yehoshua) it is impossible to explain that the case is that the father passed away before it (the product) was stolen, for if so (that the father passed away before the time of the theft) the responsibility to safeguard the product has left (from the father-watchman) and the hairs have no obligation to pay (in a case of theft), and since they are exempt from payment, even in a case that they paid on their free will, they were not rewarded with the double.