How many did you get for £40?
I pay £4.50 for my design to be stitched on any item, bought 20 polo shirts of Ebay for £40.
Been wearing them for 8yrs never been stopped and asked for a card
although I often get accosted in the car park as I return to my van.
I think they are about constant reinforcement of your name, when you are cleaning every time the customer looks at you they see your name, so in the future when it come to remembering who you are they have a greater chance.
Same goes for in the supermarket or walking down then street, the more chance people have of seeing your name the more chance they will remember it when it comes to needing a carpet cleaned.