If there is any peeling — and there usually is somewhere — it's essential to scrape off any loose paint. This doesn't just mean the parts that are already separated from the wood and ready to fall off on their own. Each spot where paint has peeled loose needs to be scraped thoroughly until you can no longer get the sharp corner of a putty knife under any of the surrounding edges of paint. Then, the bare spot needs to be sanded until the paint edges are smooth.
A true professional understands that it is his or her responsibility to provide a quality job for the homeowner. Professionals also know that attention to detail is a part of the job. While a homeowner might leave a bit of paint on the window pane, a dedicated interior painter for hire will make sure that these small details are handled properly, because a perfect job is the best calling card.