We offer a curtain service. We take them down, take them to the dry cleaners, take back & rehang. We take out hooks & other fittings. We tell the custy's which dry cleaner we use. We charge 50% more than the dc's would charge, and we get a 50% discount from them, so our gp is about 66%. Lined curtains just over £1.00 per sq ft.
They can still shrink, often do, in fact. Last job was worth total £620 gross inc vat, and that was an ordinary lounge in a nice-ish bungalow.