Exactly what do you mean by Fruit Juice - "Juicy Juice", Frozen Fruit Concentrates, Bottled 100% Fruit Juices, Bottled Concentrate juice?
Personally, just my thing, I would avoid any juice that is just identified as "100% Real Juice" because 9 times out of 10 those are a mix of 'real' juices but primarily Apple, White Grape, and Pear juice with the "Named" juice as the least predominant juice in the container. You can still get a good wine but it will in fact be a blended wine.
A good example would be the different approaches two wine base suppliers take:
Vintner's Harvest = 100% the Juice name on the label - If it says it' a Blueberry wine base then it is 100% blueberry juice
Here's the Ingredient list from their Blackberry wine base: Blackberries and Water
(Makes 3 or 5 gallons but I always make 3 gallon batches from one can.)
Current price on Amazon - Price: $33.94 + FREE Shipping
Vintner's Best = A blend of Apple, White Grape, possibly pear, Natural Flavors.
Here's the ingredient list from their Blackberry wine base: Fermentable Apple, Pear, Blackberry, and Grape Juice Concentrates, Water, Citric acid, Natural Flavors
Current price on Amazon - Price: $56.99 & FREE Shipping
Folks use either one and I've not heard complaints but if you look at the ingredients list that tells you what you are really paying for.