I have no clue what the Formula is but some Venders only ever have like 8 items and some have 20 items. But if they have a lot of items and you screw up and sell them something you didn't want TO sell, you never see it in their inventory if they have a lot of items. So you can't buy it back if you wanted to.
And I am sure ALL of us have had that happen one point in time or more.
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