Most modern pairings of gods with planets were assigned by later writers. Inanna and Venus is different: the identification is made in the Mesopotamian sources themselves, in their own language, from an early period, and it is one of the very few god-to-planet links in this whole subject that can be shown to be ancient rather than modern.
Venus behaves unlike the other planets visible to the naked eye. It appears as a brilliant morning star for a stretch of months, disappears, and returns as an evening star, and the alternation is regular and easy to notice without instruments. Mesopotamian observers matched it to Inanna, and the doubleness was read as an aspect of her rather than as a puzzle: the goddess who is mistress of love in the evening and of battle in the morning. Hymns address her as the star, and one of the oldest surviving astronomical documents, the Venus tablet of Ammisaduqa, records twenty-one years of the planet's risings and settings as omens, compiled under a king of the First Dynasty of Babylon in the seventeenth century BC.
The line from there to later astrology is real and traceable. Akkadian-speaking Babylonians called her Ishtar and kept the planetary association; Levantine peoples had Astarte, also linked to the evening star; the Greeks identified Astarte with Aphrodite, as Herodotus already does in the fifth century BC; and the Romans rendered Aphrodite as Venus, which is the name the planet still bears. The English word for the planet descends by a chain of translations from a Sumerian goddess.
That chain is worth stating precisely, because it is the exception that shows what the rule usually looks like. Each step of it is documented. Most claimed correspondences between pantheons have no such chain behind them and are simply matches made by modern writers on grounds of resemblance.