פירוש על קידושין 36:8

R. Amram explains that this girl became a widow through designation. I.e. she was sold and then designated to be the wife, and then the master or his son died. The Talmud adds that the original money, the sale, was not given as kiddushin, and therefore, new kiddushin money would have to be given when he designates her. Thus the sale was not “kiddushin” and therefore the father can betroth her again should she be widowed.
[The Talmud will return to discussing the issue of whether the original money counts as kiddushin later on daf 19]

It cannot be that the designation effects marriage, because once a girl is married her father can no longer sell her off.