Here is my take on it....
Right now, I book the appointment and then get their info, email, phone.
I send them this agreement. I will not consider the appointment booked until they fill it in and submit it. That is a confirmation of the appointment.
http://www.callthatgirl.biz/computer-support/client-agreement-form/
Then I call them at the appointment time.
After the appointment, I tally up the minutes and tell them the bill and that I will accept their credit card. I use paypal virtual for this. I pay $30 a month and a few extras, but it's worth it for me.
I haven't ever been screwed over. I kinda feel I build a relationship with them during the call, but as I grow...I do have worries.
I will be hiring a tech in the next month and with that, I will probably start doing a pre-auth on the cc when I book the appointment with new clients only, and those that don't come from a secured source (referral, connected to me, etc). Like someone off Google, whatever.
What I find just amazing, is that I will have 500 clients by the end of January and with all the repairs I do, I have almost given no refunds or been screwed over. One bad check.