Actually, wouldn't that be a problem with every extract you buy?
In addition of course, to the main problem of most of them tasting artificial.
Well, at least with the homebrewing varieties, you have a better chance of finding another brewer who has used it and might be able to say "2 oz for a faint fruit flavor, 4 oz for a bigger one". With these extracts online, some of them are ultra concentrated and you'd have to find a way to adjust it. The bottom line on their taste is that LD Carlson extracts are all nasty, period. The Crosby & Baker versions are much better. I also found McCormick natural raspberry extract at the grocery store and it was much better and different than anything else I have tried. It's the stuff that they use to make raspberry brownies & such. Here's a
link to some of the extracts they make. I made a beer with the raspberry extract and it was really nice flavor & aroma-wise. They have cinnamon, lemon, orange, strawberry, raspberry but... no blueberry.