As I have mentioned previously, whilst on a training course some years ago there was a bloke there who did a business studies course before he started up. This was to obtain funding from The enterprise board or whatever it was at the time.
Anyway as part of his course he had to carry out market research. At a loss on what to do, the advisor advised him (thats what they do

) to stand outside a supermarket and ask people if they had ever had their carpets cleaned.
What was interesting was out of those that had cleaning carried out in the previous 12 months, I think it was 80-85% couldn't remember who had done it.
Proof if ever why you need to keep in regular contact with your customer base.
Ps stickers under the sofa cushions, with waterproof ink. Take a leaf out of Servicemasters book.