Is it proper grammer to end a sentance with the word it?

Their website would allow the customer to look at the items before coming to the store to purchase it.

I would use it.
What does "it" mean in 'It is raining'? Emotion: smile
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This is one of the uses of this pronoun. It's used to fill the place of a function (generally the subject) but has little or no meaning.

It is frequent in weather and time expressions:

It's awfulty hot in here today!
It's a bit late now.. Emotion: wink
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But 'items' is plural. Is it correct to refer to it with 'it' then?
No, it's not correct. It should be: "them" (the items).