Do you know if the client has put the quote out to other window cleaners?
I'd bet they have, judging by the quote they want from you.
Now, remember, you should quote more than what you would if you were using ladders; according to some!

Maybe some of the older members here would suggest you quote as if you're still on ladders but using a chamois; so quote REALLY REALLY high in that instance.
But I'd say you've got to quote on the cheaper side, if you want the job, then cut-all-the-corners you can to make the job profitable; but still a nice job.