David over the years we have cleaned a lot of curtains and the main thing is knowing what fabrics will respond best to the system you are using. Many you will find, particularly cotton prints will come up great with fabric restorer. A lot of curtain fabrics are not pre-schrunk and steam can cause this to a greater extent on some fabrics, so you need to identify when that might create problems. You also need to get your customer to sign a disclaimer against that and the egageration ( I told myself 1000 times to learn how to spell eggagerate) of sun fade. Many dry cleaners use these and you could get a copy from them. We have a set of terms on the back of our curtain quotation and all work is taken on those terms. If you want to have a chat give me a call on 07788621555 as I do not have the time to type too many details
Peter