Oldie but a goodie...

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The word "there" can appear as a pronoun, as in “over there".

"Their" is a possessive pronoun. In a phrase like “Susan and Bill's car,” it could be used to to make a new phrase: “their car.”

”They're” is a contraction of “they are.”
“They are” should always be able to replace “they're.”

Extra credit: It's "I'm looking for an M3" not "I'm looking for a M3".