Look at the ingredients on that label you posted You are buying a BLEND of Apple, Pear, Blackberry and Grape juice AND Corn Syrup. Look up Vintner's Harvest Wine base. IF it says it's blackberry it's 100% blackberry not added sugar or other juices. Might be a bit more (1 can makes 3 gallons) but your are getting the real deal. Others have used and been happy with what you are looking at - I'm just a stick in the mud - That label you posted doesn't say what percentage of each juice is int there so it could be just 10% blackberry or it might be more or less, there is no way of telling. You can be sure that it's not the primary juice in that container.
For price comparison On Amazon:
Vintner's Harvest Blackberry Wine base is $33.94 for 96 oz
Vintners Best is $51.64 for 128 oz
2 Cans of Vintner's Harvest will make 6 gallons of a very solid flavored wine so $67.88
1 Bottle of Vintner's Best is supposed to make 6 gallons of Blackberry wine.
You decide a 100% Blackberry Wine or a Blended Apple, Pear Blackberry, & Grape wine.
I started making my own wine because I couln't find a 100% Fruit wine. They were all blends of other juices and the flavor named on the wine bottle ingredients wasn't even the primary fruit/juice used for that wine. Started with my own Blueberrys and have made 4 batches of wine with the Vintners Harvest wine bases. 2 x Black Currant, 1 Plum, and 1 Red Raspberry. Have 2 cans of Wine base on the shelf to use this spring. Another Black Currant and Elderberry.