Thanks for all the suggestions.
I had mentioned to the customer that one option could be an invisible

repair which I have seen done before and very good it looked too, where a flowerpot had rotted the carpet underneath.
The only problem is that the room has no cupboards where a spare piece could be found to use.
On a plus side for the customer, there are various other stains on the carpet which are just as bad and look very aged. Just not pink

I said that I'll have another go at reducing the damage and they can use the fact of the other stains to barter with when they decide to move out.
The carpets were 'supposedly' cleaned by another cleaning company

prior to them moving in just before christmas, but from what I've seen they didn't do a brilliant job.
Finally, the customer has rung me again to say that her son has now got shoe polish over the lounge carpet and rug

I'd better set them up with a Direct Debit

Les