Yeah I'm the same normally I let them come to me from word of mouth but my round needed a quick boost so I went looking for them. Your right though getting customers from within the circle of customers you have is always better.
ALWAYS ALWAYS ALWAYS did I say ALWAYS? ... charge 50-100% extra for a first clean.
Here's how (after telling and reminding them that you only do regular work):-
You: How long since they were last done?
Her: six months/a year/cannae remember ...
You: Well they will need bringing up to scratch and my normal monthly amount is £10 and two-monthly it's £12.50 but for the first clean it's £20.00.
RESPONSE A)
Her: Ooh err um
You: B'bye now!
RESPONSE B)
Her: That's fine
You: I hope you don't mind me saying, but I have had experience of one or two shifty customers who get me to clean the windows once or twice and then cancel because they only wanted a "one-off"; I don't mind whether you are a monthly customer or a two monthly one but those are my terms.
Her: No, I understand, carry on.
Even this isn't foolproof but instead of a fifty/fifty chance of getting a messer it will be one in ten.