I reckon it will be an old spill come back to the surface.
The darker patch is not a shaddow either,it`s where the sun has bleached it,sofa was on top of it.
That`s what i am going in armed with !
Only charged them £48 quid too,they have one of my 20% off vouchers,i have been doing the odd bit for them over the last 4 years,so hope this does not put them off.
In reality though,the carpet was trashed,as you can see from the pics,vanish central.
Did another one today,sick on white carpet,charged £40 for about 15 mins work.
Asked cust what they had done,oh we tried vanish,then tried to steam it out with our steamer,i said there really is not much point in me even getting the machine out,but i will just to show you it`s permenant !