אמר להו רב הונא להנהו אוונכרי כי זבניתו אסא מעכו"ם לא תגזזו אתון אלא לגזזוה אינהו ויהבו לכו מאי טעמא סתם עובדי כוכבים גזלני ארעתא נינהו
Apropos the unfitness of four species acquired through robbery, the Gemara relates: Rav Huna said to the merchants [avankarei] selling the four species: When you purchase myrtle branches from gentiles, don’t you cut them off the tree? Rather, let the gentiles cut them and give them to you. What is the reason for this advice? It is because typical gentiles are land robbers,
וקרקע אינה נגזלת הלכך לגזזוה אינהו כי היכי דליהוו יאוש בעלים בידייהו דידהו ושינוי הרשות בידייכו
and land is not stolen. When one seizes land, the land remains the property of its original owner, even if that owner has despaired. In this case, there is concern that these myrtle branches were stolen from Jews. Therefore, let the gentiles cut the myrtle branches, so that the despair of the owners will bewhen the myrtle branches are still in the hands of the gentiles and the change of possession will be accomplished through their purchase and transfer into your hands. The combination of owner’s despair and change of possession will render the myrtle branches the property of the merchants, and it will not be a mitzva fulfilled by means of a transgression.
סוף סוף כי גזזו אוונכרי ליהוי יאוש בעלים בידייהו ושינוי הרשות בידן לא צריכא בהושענא דאוונכרי גופייהו
The Gemara asks: Ultimately, even when the merchants cut the myrtle branches, let it be a case of despair in their hands, and the change of possession is accomplished through the purchase and transfer of the myrtle branches into the hands of the buyers. Why did Rav Huna advise them to have the gentiles cut the myrtle branches? The same result is achieved through their sale. The Gemara answers: No, it is necessary for Rav Huna to advise the merchants to allow the gentiles to cut the myrtle branches only with regard tothe myrtle branches of the merchants themselves, which will not undergo another change of possession. The only way to ensure that the merchants are fulfilling the mitzva with myrtle branches that belong to them is to have the gentiles cut them and have the change of possession accomplished through the purchase from the gentiles.
Now Tosfos in that sugya [ד"ה הא] says that one may not make a bracha on something that was originally acquired with an aveirah even if now it legally belongs to the person. [שאני ברכה דאיכא נמי הזכרה לשם שמים].
So the gemara solved the problem of the buyer not owning the hadas but how can the person make a bracha??
