A customer took an esrog to show his Rav. I stipulated that if he will not purchase it, the esrog should be returned that day. However, he did not return it until after Yom Tov when it was obviously worthless.

Q: Is he obligated to pay, considering that his actions caused me a loss?

A: The first issue to consider is hezek she’eino nikar — indiscernible damage (i.e., the object was not discernibly altered but something was done to make it prohibited). Shulchan Aruch (C.M. 385:1) states that one who causes hezek she’eino nikar is not liable because it is not considered damage.

However, Chazal instituted that one who intentionally causes indiscernible damage is liable. Nevertheless, this enactment is limited to damage that one actively causes. If the damage resulted from inactivity, the thief is not liable and may return the damaged goods (harei shelcha lefanecha) without any further penalty since the thief did not damage the goods; he merely prevented salvaging them (Ramban, Dina D’Gormi, see Shaar Mishpat 176:4). Thus, one who stole and retained possession of chametz through Pesach, thereby causing it to become prohibited, may return the chametz without any further penalty (C.M. 363:1).

Similarly, a thief who stole a coin that went out of circulation may return it to the owner without further penalty. Some authorities contend that the exemption is limited to where the coin remains valid currency in another country, but if it was invalidated entirely it is considered discernible damage and the thief is liable (C.M. 363:1). Others contend that even if the coin is invalidated altogether it is categorized “indiscernible damage” and the thief may return the coin (Rema 363:1 and Shach 363:5).

According to some, returning a stolen esrog after Sukkos is subject to the debate concerning invalidated coins (Pischei Teshuvah 363:1 and Mishpat Shalom 200:7). Others contend that one who steals an esrog is certainly liable, since everyone recognizes that after Sukkos the esrog lost its value and thus the damage is discernible (Beis Shmuel Acharon, cited in Pischei Teshuvah, ad loc. and Nachlas Tzvi 291:24: see Ohr Same’ach 2:14 for an explanation).

The above discussion relates to whether beis din could compel someone to pay for indiscernible damage, but it would seem that one who is negligent has a moral obligation to pay (see Imrei Binah, Pesach 12). Consequently, in your circumstance, although he may be considered a shomer rather than a thief (see Ketzos 294:1), many authorities maintain that a shomer is also exempt when it is an indiscernible damage (see Shach 363:7). Therefore, if the esrog indeed lost value due to his delay in returning it to you, his liability is subject to the above debate concerning indiscernible damage. However, all authorities agree that if he was negligent he would have a moral obligation to reimburse you for your loss.

This analysis assumes that when he took the esrog it did not have a set price. If the esrog did have a set price, he is liable for the full amount, since taking something on consignment is halachically a purchase with the allowance to return it (C.M. 200:11; see also Nesivos 186:1). It is therefore understood that the allowance is limited to it being returned in a timely fashion. If his delay prevents you from selling it for a satisfactory price, he forgoes the right to return it and the sale is now final, so he must pay you the agreed-upon price (see Hayashar V’hatov 7:9 and 14:15).