Related for Demai 3:2
הָרוֹצֶה לַחֲזֹם עֲלֵי יָרָק לְהָקֵל מִמַּשָּׂאוֹ, לֹא יַשְׁלִיךְ עַד שֶׁיְּעַשֵּׂר. הַלּוֹקֵחַ יָרָק מִן הַשּׁוּק וְנִמְלַךְ לְהַחֲזִיר, לֹא יַחֲזִיר עַד שֶׁיְּעַשֵּׂר, שֶׁאֵינוֹ מְחֻסָּר אֶלָּא מִנְיָן. הָיָה עוֹמֵד וְלוֹקֵחַ וְרָאָה טֹעַן אַחֵר יָפֶה מִמֶּנּוּ, מֻתָּר לְהַחֲזִיר, מִפְּנֵי שֶׁלֹּא מָשָׁךְ:
One who desires to trim leaves of vegetables in order to lighten his burden should not discard [the leaves] until he has tithed them. If one buys vegetables from the market and then decides to return them, he should not return them until he has tithed them, since they [the bundles] lack nothing but counting. However, if he is standing and selecting [the vegetables] and then sees another bundle that is of better quality he may put return them [without tithing] because he has not yet grasped them [in a manner of acquisition].