Is it a condition for the possession of a purchased item to have it enter inside the warehouse, or is it sufficient to receive it in front of the company?
The correct possession of a purchased item takes place when it is conveyed from the place of the seller to the place of the purchaser. This is because the Prophet (peace be upon him) prohibited selling goods at the same place of their purchase before traders convey such goods to their own baggage.
The foregoing is narrated by
Abu Dawud and
Conveying the sold item by the purchaser to a place that does not fall under the disposition of the seller is sufficient in this regard for
Ibn `Umar (may Allah be pleased with them both) said:
We used to buy food from riders without measurement, then the Messenger of Allah (peace be upon him) prohibited us from selling it until we transfer it from its place (i.e. the place where it was bought)
and in another narration:
During the time of the Prophet (peace be upon him) we used to sell food, and Allah's Prophet would send someone to us to order us to transfer it to another place first before selling it
People used to purchase food from the caravan and the Prophet (peace be upon him) used to send them a person who would forbid the riders from selling that food until it was transferred to the place of sale
and: (Part No. 13; Page No. 259)
I saw people being beaten during the lifetime of Allah's Messenger (peace be upon him) in case they bought the foodstuff at random (without weighing or measuring it), and then sold it at that spot before transferring it to some other place.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.