I came across this legal phrase in chapter 38 of Wheelock’s Latin. Apparently, the meaning is "He who sells the same thing twice is fraudulent. I took duobus to mean “to two people.” I am a little stumped. Does the dative or ablative have here the sense of “two times, twice”? I cannot find that in the grammar books.
Take a step back. If you sell the same item to two people at the same time you are selling it twice and it’s fraud. The English translation you quote captures the meaning of the Latin but it is not a literal translation.
Thank you very much. Now it is clear to me.