Loose threads in new clothes
Short answer: A loose thread is almost always a thread end from sewing and not a fault. Cut it, never pull it.
Why they are there
When a seam is finished, the thread is cut off leaving a small tail. Some of those tails survive the inspection. It says nothing about how well the garment is sewn.
How to deal with them
Cut the thread with scissors close to the fabric. Never pull, because you can open the seam from the inside and make a hole that was not there before. See bamboo t-shirts for men.
When it is not a thread end
If the thread is a loop coming out of the fabric itself, it is a pulled stitch. Push it back with a needle from the inside rather than cutting it. See bamboo clothing for women and bamboo underwear for women.
Frequently asked questions
Can you make a claim about loose threads
Rarely. It is cosmetic and not a functional fault.
What if there are many
Then the inspection was careless. Cut them and check whether the seams are otherwise even.
Do more appear over time
No. New loose threads after wear mean a seam is coming apart.