Vechi Timkeru: What nusach in Onkelos, selling or buying?

In parshat Behar:

יד וְכִי-תִמְכְּרוּ מִמְכָּר לַעֲמִיתֶךָ, אוֹ קָנֹה מִיַּד עֲמִיתֶךָ--אַל-תּוֹנוּ, אִישׁ אֶת-אָחִיו.

14 And if thou sell aught unto thy neighbour, or buy of thy neighbour's hand, ye shall not wrong one another.

In Onkelos, we have the translation as:

כה,יד וְכִי-תִמְכְּרוּ מִמְכָּר לַעֲמִיתֶךָ, אוֹ קָנֹה מִיַּד עֲמִיתֶךָ--אַל-תּוֹנוּ, אִישׁ אֶת-אָחִיו.

וַאֲרֵי תְּזַבֵּין זְבִינִין לְחַבְרָךְ, אוֹ תִּזְבּוֹן מִיַּד חַבְרָךְ--לָא תּוֹנוֹן, גְּבַר יָת אֲחוּהִי.

with tezabbein. This is correct, for the intense pattern is used to mean sell, while the kal is used for buy. Shadal, in his Ohev Ger, notes this, and notes incorrect variants:

וַאֲרֵי תְּזַבֵּין -- of the kaveid construction, as a language of selling, except that it is singular {despite the plural in the Hebrew original} to make it equal to עֲמִיתֶךָ which follows it; and in most of the sefarim, תזבּנון, and this is an error, for it is a language of purchasing.

See also this post about buying and selling in Aramaic, as it occurs in Chad Gadya.

However, I am not so sure I can agree with Shadal's assertion that תזבנון is in error, and is a language of acquiring rather than selling. Note though, that he puts in only the dagesh in the bet but leaves out all the other nikkud. As we have it in our Mikraos Gedolos, it is tezabbenun, with sheva under the tet and bet, a patach under the zayin, such that the dagesh in the bet is a dagesh chazak. This is the kaveid form, not the kal (tizbenun). Compare it to the kal forms in the Targum in the verses immediately before. And it has the benefit of matching the plural form found in the Hebrew, such that we need not resort to the slight difficulty of Shadal's explanation that there was an attempt to bring it into accord with amitecha.