Sukkah Chapter 3, Mishnah 11. Our Mishnah continues to deal with the details of reciting Hallel, and then moves on to discuss purchasing a lulav and esrog in the Shemittah year.
Repeating the verses in Chapter 118:
One of the chapters of Hallel is Psalm 118, which opens with "Hodu laShem ki tov" and also closes with "Hodu." Most of the verses in this chapter come in pairs: two consecutive verses that deal with the same idea:
"Hashem li lo ira mah yaaseh li adam" - and following it: "Hashem li b'ozrai va'ani ereh v'sonai".
"Tov lachasos baHashem" - and the verse after it likewise opens with the same theme of trust in Hashem.
"Kol goyim s'vavuni" - and following it: "Sabuni gam s'vavuni". And so on throughout the chapter.
Toward the end of the chapter, however, beginning with the verses "Odcha ki anisani vat'hi li lishuah", "Even ma'asu habonim haysah l'rosh pinah" and "Me'eis Hashem haysah zos hi niflas b'eineinu" - the verses do not repeat themselves in the manner of the verses that preceded them. For this reason, in certain places the custom developed to repeat them when reciting Hallel, in order to complete the pattern of doubling found in the chapter.
Regarding this the Mishnah says: "Makom shenahagu lichpol - yichpol" - in places where the custom took root to repeat the verses from "Odcha" onward, one should follow the local custom. "Lifshot - yifshot" - and in a place where the custom is to say them only once, one says them once. Our custom, of course, is to repeat them, as it appears in the siddurim we have.
Similarly, "L'varech acharav - y'varech" - the berachah recited after Hallel also depends on the local custom. The berachah before Hallel, however, does not depend on custom at all, but is recited everywhere and by everyone. And the general rule: "Hakol k'minhag hamedinah" - everything is determined according to the custom of that place.
Purchasing a lulav and esrog in the Shemittah year:
From here the Mishnah moves to another topic connected to the lulav. The halachah is that in the Shemittah year, once a given species of produce is no longer available in the field, there is an obligation to remove from the house any produce of that species as well - this is the mitzvah of biur. Once the time of biur has passed, that produce becomes forbidden. Ignorant people were suspected of not observing this mitzvah properly, and therefore one could not purchase an esrog from them.
These are the words of the Mishnah: "Haloke'ach lulav mechaveiro bashvi'is" - one who buys a lulav from his fellow in the Shemittah year, where there is reason to suspect that this person does not observe the laws of Shemittah properly, "nosen lo esrog b'matanah" - he must receive the esrog as a gift, while for the lulav he may pay.
There are two reasons for the distinction between the lulav and the esrog:
The counting of the years: The year that counts for the lulav is not the same year that counts for the esrog, because of the way the years are reckoned for the lulav.
The lulav is not a fruit: The lulav is considered a piece of wood and not a fruit, and therefore the laws of Shevi'is do not apply to it, and it may be purchased without any concern. The esrog, by contrast, is a fruit, and there is reason to suspect that the laws of Shevi'is apply to it, and therefore he can only receive it as a gift.
The Mishnah concludes with the reason for this: "L'fi she'ein rashai loke'ach bashvi'is" - there is no way to purchase an esrog in Shemittah, unless the buyer includes its price within the price of the lulav. For he may pay for the lulav, and may even raise its price and pay a high sum for it in order to obtain the esrog, provided that the payment is for the lulav and not for the esrog.
In summary: In this Mishnah we learned two matters. First - repeating the final verses of Psalm 118 and the berachah after Hallel depend on the local custom ("Hakol k'minhag hamedinah"), while the berachah before Hallel is practiced everywhere. Second - one who buys a lulav from his fellow in the Shemittah year gives him the esrog as a gift and raises the price of the lulav, because the lulav is not subject to the laws of Shevi'is while the esrog is a fruit, and one may not purchase it in Shevi'is.