A: Lechatchila, tevila should be done after paying for (acquiring) the keilim. Bediavad, tevila is repeated without a Bracha.
The Taz  notes that Tevila is required when utensils (requiring tevila) are "transferred" from the possession of a non jew to a jew. However, a retailer that purchased keilim from a non Jew with the intention to resell them, does not have an obligation to tovel them. Consequently, toveling does not change the status of the keilim until the "end user" purchases or "acquires" them. It is only after this acquisition, that the obligation to tovel arises.
However, there is one caveat. Some authorities hold that once a potential buyer decides to purchase an item, and both parties agree on the sale, the buyer might be considered as having acquired the product. This would automatically trigger a requirement on his part to tovel the item, (since it is technically his already) and if he were to do so even prior to actually "paying" for the item, it would be considered as if he toveled his "own" item.
The Minchas Shlomo applies this to a case where the item was intended as a gift. Since, the purchaser was not acquiring the item for himself (as his intent was to gift it), he was under no obligation to tovel the item, and as such the tevila should be repeated, without a Bracha.