Many many small and fly by night dealers recycle old mattress stuffings or even cover existing old mattress's.
You see all these carriers hauling around old mattress with stains and bad looking stuff. Ever wander where they go and what happens to them?
You may have an old recycled mattress or stuffings that was chemically cleaned or impregnated with a chemical smell to block the old smell.
Other than sprinkle the mattress with alot of baking soda or leaving it out side for days and days, you are stuck with it.
If it was mine, I would toss the mattress and buy a "new" one from a reputable dealer and go with that. You will have a better "peace of mind". I would.
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