Some guys would clean internal windows for one and a half times the value of cleaning the outsides. Personally I wouldn't clean the insides for twice the price of cleaning the outsides. In the time you've cleaned the insides on most jobs, (even when asked to clear the sills prior to internal clean), with all the faffing around, you could have easily cleaned twice as many external windows. Internal jobs aren't regular with most customers and you have to arrange a day and convenient time to be there for access. If anything goes missing or is misplaced who gets the blame, not worth it for the inconvenience or financial side of things