It really depends on what treatments and how much they are spending.
If they only want a manicue and they live more than 5mils away i would charge a min fee.. whatever your average per hour is how one way you could work it out, as you have to consider traveling time & petrol there & back, howerever if they are spending £30 upwards and your going to be there a while, i wouldn't charge. but i would make it clear when you get there, that if they DO only want one treatment in the future there will be a charge, but if they get a few friends together there wont be. That way it'l boost your clientell coz they'l want to save money.
Hope his helps
CAZ X