I already know that boxed or cartoned juice is less likely to have been freshly squeezed, but what about transparent bottled juice especially in the refrigerated section of supermarkets?
This isn't exactly scientific but..
Taste. Specifically looking for the taste difference between pasteurized and un-pasteurized juice. Pasteurized orange juice has a distinct tart taste that just isn't there with fresh juice.
I guess it depends on your exact meaning of "fresh", but if it hasn't been pasteurized then it will have a shelf-life of only a few days.
The legal specifics of the terms will vary from country to country, so if you have one in mind then you might have to mention that. Although as you hinted at, the legally defined terms are often side-stepped and might not be much use.
According to Juice and Cider: Make Sure They're Safe
Some grocery stores, health food stores, cider mills, and farm markets sell packaged juice that was made on site that has not been pasteurized or processed to ensure its safety. These untreated products should be kept refrigerated and are required to carry the following warning label:
WARNING: This product has not been pasteurized and therefore may contain harmful bacteria that can cause serious illness in children, the elderly, and persons with weakened immune systems.
So if it carries the 'has-not-been-pasteurized' warning then it is freshly squeezed.
Nothing beats experience. Have you ever tasted juice just squeezed from oranges or apples? Nothing else compares to this. In restaurants or shops you often get "freshly squeezed" juice that only once was freshly squeezed - a long time ago. If you know the taste of freshly squeezed juice you will never be fooled again.