What helps with this is, before going in, you ask yourself if you're prepared to walk out if she's not what you're expecting.
If she's not, just commit to walking out. Just say fuck it. Stand your ground.
In the past, I've failed to walk out of catfish situations. The first couple times it feels a bit difficult. But man, you're really proud of yourself when you still have your [whole] wad of cash, where you can regroup instead of losing a chunk of your money, feel like you got nothing for it, pissed off because you're still horny. Now you can just go to plan B.
I've been on both sides...didn't back off, paid to bang a fat, ugly chick that IRONICALLY I wouldn't fuck for free and felt like a dumbass afterwards. I've also walked out a few. Of those, I've walked out with all my cash, but a time or two left a 20.
I've also had these where the girls weren't the girls in the pic, but was still fine as hell...so I stayed.
Sometimes these girls I guess underestimate their hotness and chose a lesser pic to steal. Too often it's the other way around, though.
In a nutshell, try being ready to walk out going in. It's easier to follow through this way.
Of course, if she's actually hot, simply abort the bail out and plow her.