The object itself has a lot to do with the relative success of this technique. Best case scenario is a good, straight-on product shot. This eliminates the need for oblique reversals which take a lot of time, and need to have a perspective slant in order to look convincing.

 
Creating the reflections

Let's use this shot of a Pentax camera.

Note I've carefully cut it out of the background so no slivers of white are showing. Mistakes in removing the background will be glaring once we build the illusion.

To make the illusion, we need a much larger expanse of background.

Here, using the Crop tool, we can drag the handles beyond the image area and visually estimate the size we'll be needing. Once you commit the crop, the canvas will be expanded to fit the size indicated.

Since any reflection into glass or a liquid is a 'mirror' image of the original, we have to create that copy.

The easiest way is to merely float a copy (Cntrl/J or Cmd/J) and with the Move Tool (Tap V) drag the top, center handle down below the bottom. I'm going to leave the dragged image just a bit compressed. This lends a bit more realism to the scene.

At this point we'll need a background to reflect the image off of. Some people like smooth, level graduated backgrounds, and others like spotlighted. Apple uses sort of a spotlighted background, note where the 'hot spot' is in their images. (Note, if you're using a white-out background, then no graduations are necessary.)

We'll use a Black to White graduation first, just for the sake of this demonstration.

I'm holding the crossover point of the gradation to just below the horizontal center of the scene, and the lighter part never achieves white. I accomplish this by starting the gradient about 20% down the scene, and dragging about 20% beyond the bottom edge of the window. This brings a 20 to 30% gray to the edge.

Now we can begin working with the reflected image.

First set the transparency. I used about 40%, but that will change as we move along.

To make the reflection realistic, as it moves away from the object across the glass surface, it gets more faint. So we'll need to simulate that "fall-off" by using a layer mask.

Select the reflection layer, and then click on the Layer Mask button. You'll see the white mask appear next to the layer thumbnail. Click in the Layer Mask thumbnail, and its borders will become doubled to indicate it's selected.

Now, using the gradient tool drag a tight, quick gradient from black to white. You'll notice how the black masks image and the white allows it to show. The reason I'll use a mask here is to adjust the amount of transparance by moving the actual mask up and down.

Turn off the lock links between the thumbnails, make sure the mask is selected, and with the move tool, you can drag in your image window to adjust where the gradient falls on the image. Very handy.

At this point we're done.

I think the black and white is very elegant, but a little too stuffy and formal. Let's add a bit of color to offset the steely grays of the camera. Create a new layer and simply fill it with the color you like.

The last (and optional) step is to add a Gaussian Blur to the reflected image. In realism, the reflection will never be perfectly clear. While you may like it, and keep it, I like to throw it off just a bit -- so I'll ad the most slight blur.

The amount of Blurring depends on resolution. More blur for higher resolution. But for the sake of loading times for my captures, I've kept this a low resolution image, so .5 or so blure does the trick.

You're done.