This Korean saying is essentially the direct opposite of "never judge a book by its cover."
You can probably consider the following in addition to some wonderful suggestions in comments
What you see is what you get
The product you are looking at is exactly what you get if you buy it
It is a popular phrase in the computer industry. It is abbreviated to WYSIWYG (pronounced as "wiz-ee-wig"). For instance, if you are printing a document, whatever you see on the computer screen will be exactly printed as it is without any changes whatsoever.
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Here are a couple expressions that come close:
"If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck."
"Where there's smoke, there's fire."
Actually, there are a number of Google hits for "If it looks good, it tastes good," though that expression isn't familiar to me. Note the similar Japanese proverb, "Food should feast the eyes as well as the stomach."