Second hand old King size mattress

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We have had this king size pocket-sprung mattress for about 15 years. its was expensive and a good brand. it is by Hypnos and has all fire safety labels attached. After 15 years we decided probably time for a new mattress. As you can see from the photos the cover is marked - not by anything dodgy, no idea what - probably spilt tea or moisturiser/ suncream?!! There is also a rip in the cover only which we patched ( see photo) and put as the side that faces down and had no problems with this. All this explanation is so that we don't let someone have it and then they don't like the look of it. We were sleeping on it until last night so not been in storage etc. its old and discoloured but free to a good home to save us having to tip it which would be such a shame. Only genuinely interested people please