A. A used car lot: "Gulf Shore Motors".

Q. Where is it supposed to be on the show?

A. Somewhere in Miami, near a marina.

Q. When did we see it on the show?

A. In Episode 3 (of Season 2), "An Inconvenient Lie".

Dexter discovers that a used car salesman has been running credit checks on women who later turned up as murder victims.

So Dexter pays a visit to the used car lot, "Gulf Shore Motors", to check out Roger Hicks, a glib, charming car salesman who may be murdering his potential customers.

Dexter pretends to be a family man interested in buying a new minivan, to get close to Hicks.

But Hicks is so good at his job that Dexter actually winds up buying the new minivan.

While he's there, Dexter steals Hicks' comb, to get a DNA sample. But the hair on it turns out to be synthetic.

So Dexter returns to the car lot, pretending to want to buy more options, and takes the time to snoop in the salesman's office and steal more DNA evidence (a cigarette butt from an ashtray).

While there, he meets a young woman who appears to be Hicks' next victim.

Dexter returns one final time to the lot - after dark - to abduct Hicks and toss him into the back of the new minivan.

Q. What is it actually in real life?

A. A simple parking lot.

Q. Where can I find it in real life?

A. The scene was filmed in a parking lot behind Edie's Diner, a restaurant located right on the waterfront at 4211 Admiralty Way, in Marina Del Rey, CA.

This parking lot is right next to the marina, just southeast of the diner. They simply brought in some cars with sticker prices, put up a fake sign, and strung up some flags for ambiance. The "office" appears to have been a houseboat moored at an adjacent dock.

The parking lot is a bit tricky to reach.  I think it may actually belong to the yacht charter company which owns the nearby building used as the Narcotics Anonymous meeting hall, rather than to the diner itself. (That white building, with its bell tower, is actually visible in the background of some of the car lot scenes.)

This is the same diner they used for filming the interior scene of Dexter & Lila talking over coffee, after a Narcotics Anonymous meeting (in the same episode).

In 2008, the restaurant changed names.  It's now called "The Organic Panificio Restaurant & Cafe".

Here is an aerial photo of the area, with the parking lot marked (as well as the diner). And here is a map link.

Q. How the heck did you figure out where it was?

A. You can see the diner in the background of this scene (behind Dexter's head, in the third photo from the top). Once I knew where the diner was, it was obvious that this scene was shot in the nearby parking lot.