In chad gadya, we use the Aramaic root זבן. Now that I think about it, I always recall hearing both
דְזָבִין אַבָא בִּתְרֵי זוּזִי and
דְּזַבִּין אַבָּא בִּתְרֵי זוּזֵי. The obvious difference being that דְזָבִין means he bought and דְּזַבִּין means he sold. (See Jastrow)
Which one was it? Do all or most interpretations lean one way?
On second inspection, the link I cited supposedly containing דְזָבִין, was actually דְּזַבִּין. When zoomed in, the dot is visable. I next found that all other Haggadas I viewed contained only two variants. זַבִּין and זְבַן. The incorrect vocalization of דְזָבִין was taken from Wikipedia, which is, Wikipedia.
Firstly, as cited by WAF, the Frank dictionary does claim that the correct text is זְבַן, meaning sell.
However, the question still stands because a sampling of my printed collection seems to yield both results.
A בּ should not be vocalized זַבִּין for 'sell' past tense, rather זַבֵּין (based on Frank grammar, p. 59). And the past tense for 'buy' is זְבַן, as mentioned. [Although he does mention זַבִּינא as past tense she/it for sell. גדיא seems to be a female word, so it could make sense how it made it זַבִּין from זַבִּינא. Even though aba is doing the selling!]
Therefore, there are still two contenders for proper meaning among the hagadas. Buy/ זַבִּין or sell/זְבַן, and all questions questioned above in the question.