Hi Lovey, hope all has settled down now, see... we were right in saying it is best to follow your instincts but on the other hand I know what it is like to need the bookings.
Have a look at my article regarding products to avoid and aftercare advice
http://www.salongeek.com/training/182579-products-avoid-after-spray-tan-some-aftercare-advice.html
I usually do a mini consultation at the time of booking just to make sure they arent pregnant, have flared up psoriasis or allergies. Then I ask which beuaty products they use if they are unsuitable at least they have had time to get a replacement. I also ALWAYS fill in a consultation card which has a section for the client to sign agreeing that everything has been explained including how long to wait before washing, loose clothing etc etc. I have the same document as a Do's and Dont's PDF on my website and FB page. This way they have access to the information any time.
If they did not let you inspect the "problematic patchiness" by now I think it will be too late for you to see if your application or their aftercare was to blame.
I had some girls a few years ago say that they had gone patchy but when we went into the complaint properly it turned out that the one girl who had left the property directly after I left had a great tan, the other two stayed in all evening in a SWELYERTING hot house, I was perspiring packing up so they were sweating all evening in cozy winter Jammies. They hadn't taken any notice but I pointed out that they had signed the form stating that I had explained it all to them. Never saw them again but then never wanted to either. LOL
Chin up and remember that one complaint does not mean you have done a bad job, just learn to protect yourself a little better as already suggested, online booking, stating areas covered on your website, place " Do's and Dont's" document on your site and state that any issues need to be addressed within 24hrs,( pop that on your consultation card not your website eg. if they complain the next morning you have to see them that day else you cant ascertain the problem properly)