I feel your pain. I, too, bought a serta mattress from shop nbc.
It was great -- for the first 6 months then it started showing body indentations on both sides if the bed. What convinced me to buy the mattress to begin with was the 10-year guarantee. I figured I had nothing to lose. I wrote a letter to the company, then scheduled the inspector to come to inspect the mattress.
It met their parameters for defect. So the company sent me another mattress. It was never as good as the first one which was very comfortable at first; the second one was not. The following year, the second mattress was showing signs of defect, so I went through the process again.
Serta replaced the mattress again. The third being worse still. This mattress was uncomfortable from day one. I can feel my husband's every move (unlike the original mattress I purchased).
I started the return process again. However, this time, the mattress did not show the defects my husband and I were feeling. The indentations were not deep enough to warrant replacement. Our backs are telling us a very different story.
I will try again to return this mattress. However, I will not accept another replacement; I want my full purchase price back. Serta has proven to me, three times, that their product is inferior and their customer service is lacking.
I will NEVER buy another Serta product. I haven't had a decent night's sleep in 3 years.
Product or Service Mentioned: Serta Mattress.
Reason of review: Bad quality.