When is selling prohibited if Jumu'ah prayer is held in mosques an hour or two before the Dhuhr athan?

The time for Friday prayer (Jumu'ah) is the time of Dhuhr according to the majority of scholars. Therefore, it is safer to perform it at that time to avoid disagreement. If the criterion is the mosque where the Friday prayer is performed, then you are not required to refrain from selling if you will not be praying there. However, if the criterion is the first call to prayer (adhan) in the town, then you must refrain from selling when you are certain of the adhan. If you are unsure about the adhan, the default is that it has not occurred, and selling is permissible.