I suspect the problem is happeing during shipping or in some manner how you are handling the plant.* Is it arriving bare root?* If so, how long do you soak it in water?* Does the packaged plant sit in sun for a long time before it's unpacked?* How do the plants look in the package?* Their shipping references aren't the best.
Most potting soils are peat moss based and therefore on the acid side.* I was reading all that you did with the peat moss and aluminum sulbadworde and I'm thinking you are going to burn your plant.* What I've found with peat moss is that though it does retain moisture, once it dries it's difficult to rewet.* It also isn't very high in nutrients.* I have a friend who purchased several of these and used potting soil mixed with compost and her's are doing fine.
I'm thinking that it's the quality of the plant material and not you.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.