Unless I'm spectacularly missing the point here, the punter walked because the OP didn't look like her pictures and therefore was not what he was expecting, not because she was too big or too small per se. Has everybody else (bar Clover and Escort38 as far as I can see) failed to spot this, or is the neverending quest to blame everything on the punter no matter what which seems to be becoming endemic here just easier?
If I was about to buy a blue car and when I arrived to collect it the one they gave me was orange I'd say thanks, but that isn't what I'd asked for. I'm sorry you're upset Sadie and I'm sure you feel horrible, but if your pictures aren't representative this is going to happen now and again and we can't seriously expect somebody to part with a large sum of money and shag somebody he doesn't fancy just out of gallantry (and if I'd been bodily shoved out of the door I wouldn't have been anywhere near as polite, and I certainly wouldn't have apologised). What punters look like has nothing to do with anything, and we all know that perfectly well - we aren't the ones paying.
I had two tellings off in a week about a month ago for being smaller than my pictures; I've dropped nearly two stone since February when I last did some pictures and as a result I've had to cobble some recent ones together sharpish. I've made mention of it in my ads and to anybody who asks on the phone since then, and nobody's walked but there was one bloke who definitely wasn't happy when he first saw me because he was expecting a curvy size 12 and didn't get one, and he had every right not to be.
Sadie I know you can't magic up new pictures out of thin air, but you can alter your ads so they're truthful, at least. You'll feel less under pressure yourself and even if it puts a few off it will attract others, and it may well avoid this happening again.