Hi,
I've been in the same position, advertising both in the British Telecom book and the local pages.
For the past eight months all I've received is calls from domestic customers in areas I don't clean. I've passed them onto other window cleaners who I know do their areas; or just said 'sorry mate - ask your neighbors who does theirs'.
However, and I don't know why, recently I've just ended up getting phone calls from five large businesses to give 'em a quote.
I've already just bagged one of them (the biggest and best - a large, posh hotel - they made me jump through hoops to get the job with method statements, risk assessments, safety policy etc), and waiting to find out if I've got the others! It means I've got the potential to have lots (and I mean lots) of inside work too. Just right for winter!
I think you MUST advertise to get large commercial work, but at the end of the day - IT'S PURE LUCK - if a potential commercial customer phones you. Remember also, if it's a large site, he (or she) will be phoning at least three other competitors for quotes too.
Then it comes down to price, selling your company and the professional image you give during the quoting period.
Well that's my thoughts, but I still am very inexperienced!