I rarely do windows without doing the inside as well. I ask 60-70 euros which is about 50 quid. Most people don't trust you unless your recognised, insured, legal etc, so referals are a must. Yes you have the furniture removal hassles, antiques, net curtains, pets drinking your water, the overshoes (which I find look more professional, & the customers presume are new everytime).
I think this is worth it for the money involved. The only trouble is juggling the customers to when they are at home. Some of them just go out shopping and leave me to it, with the money on the table. I rarely ever have to go back to get paid. Inside & out for a shop window is worth 20-25 euros (20 quid), but also using gg4 you see the benefit more than washing up liquids. I also give them the tip that cleaning with a clean teatowel will remove handmarks from glass doors, persistant marks just dab in distilled water.
Hope this helps.