hiya!
yup its happened to me (a few times) for hair colour appointments, and once for a wedding hair. iv had girls requesting prices then saying "oh i thought you were mobile, thats a shop price" and my prices arent expensive!!!
the wedding hair one was tres annoying, last minute booking for 5 bridesmaids and a bride, no time for a deposit or trial and i had been recommended to her. she requested a price which i gave her (for a sunday wedding, 7.30am start). I then had a call at 8pm the night before the wedding with her saying it was far too expensive she heard i was only £15 for a hair up (hadnt been for over a year by that time) so she was cancelling. What she actually wanted was for me to bring my prices down to £15 a head! so i politely stated the price is the price and i hope she managed to find another hairdresser by the morning if she wasnt willing to pay it as she had known the quote for a week already.
suppose my point is people will always try it on, your prices are your prices and i feel if you are doing a quality service your prices should reflect this, wether you are in a shop or mobile. Obviously dont price yourself out of the market, but just because other people are doing "minx" pedi's for say £10, doesnt mean you should. you know your products and your skills. stick with it!