Commentary for Bava Metzia 68:11

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.