Buffwipes - Pre Tan Skin Exfoliating Wipes
Try these....I get mine from Celebrity Secrets. There a bit more expensive than make-up wipes, but far better than having people come back for top-ups. I also get people to remove any deodorant with them too. One wipe should be plenty.
The problem with make-up wipes is they have moisturiser in them too, moisturiser acts as a barrier to spraytan solution hence it won't take.
Personally, I advise everyone of this first and then if they choose to ignore me its their own fault and I wouldn't offer any freebie face top ups. In fact I'd see it as a retail opportunity and be selling them a tan in a can for the face, or tan wipes from my range!