Surely any one who has there carpets cleaned is serious about looking after
there carpets otherwise they wouldn't have them cleaned in the first place

which is why businesses keep a data base, as they are already known people
who would be interested in having it done again!

And how could anyone say for definite they would be having there carpets done
at a certain time, surely people have there carpets cleaned when they need it
doing, so a mailshot is a good reminder to use you when they need it, above
someone else.
Direct marketing is a proven avenue in growing your business, nearly all small
and large business employ some sort of database and mailshot campaign. -
I think it would be difficult to guess who your potential customers would be in the future without canvassing all of them.
Regards
steve