In 1957, if you wanted to "plus up" a product shot, you reached for your airbrush.... or you reached for your staff artist, who, in turn, reached for his (most likely "his") airbrush. This was back when "photo shop" meant "a shop where photographs are worked on".
First, you'd start by taking a picture of your product, and then having a print made in large format. You know... about the size of a canvas? The photo retoucher then went to work clarifying shadowy areas, adding contrast, and generally highlighting the hell out of the product. Surfaces were made shinier. Areas of low contrast got dark outlines around objects.
Above, we see a refrigerator ad for Western Auto. I guess I'm not old enough to be familiar with the brand. But look at that fridge! Ignore the fact that the interior is molded in "intestinal pink", presumably to help you imagine how the food will look in your belly. It's been heavily airbrushed. So much so, that there is not discernible light source other than "sort of everywhere". The food products in the fridge look positively cartoony. The metal trim at the bottom has recieved the old "metal sheen" treatment.
The point was not to make it look more real. The point was to make it "ideal", which, depending on the disposition of your art director, may be "Disney style". My favorite part of this picture? The landscape outside the window. Rectangular marshmallow trees! Hooray! I want to go play outside in Picasso Grove after the photo shoot.
In case you don't like the pink interior, I'm sure the fridge was available in "avocado splatter" and "golden shower" to help you imagine your food exiting your body in various ways, if you're into that.