I have had great success with the nightcrawlers from walmart as long as:
step 1: feel the weight of the container, those that feel much lighter than the others do not even bother to open.
Step2: The containers that do feel heavier, you want to open and inspect for sickly/dead worms and while open check to see if the worm dirt appears to have a muddy consistency, it is my opinion that those that do have had water added and I will pass on them every time.
step3: after discarding step 1& 2 choices, find the heavy containers that have healthy looking worms, the dirt is moist yet not mud and you are good to go.
I bought a worm farm thru walmart online that fits in the bottom of the fridge, every now and then I will pick up a box or two of worms and add them to the farm, and let them get to farmin
I lay down a line of worm food at one end of the box, position some damp newspaper over the opening and then put the lid on....I keep worm for months, and months and months