Back in the day when I was an Amiga / Toaster / Flyter consultant (the only one in town with a clue) I had a customer who was a real pain the arse.
A friend of his was saving his screen caps in 8 seconds. My customer's computer was taking 30 seconds. The only difference between the two machines was that HIS was a stock 7.x MHz A2000, while the other guy had a 68040@25MHz/32 Meg ram accelerator on it.
He basically asked me "If I have that accelerator, will I be able to save my screen caps in 8 seconds?" I told him he'd be able to do everything the other guy was doing, but I wasn't making any promises about speed of saves. They'd be the same machines.
Now, I'd never actually seen the setup of, or used the other machine, I was going strictly by what he told me.
So, I order his accelerator, install it, get everything setup right, and guess what? His screen cap saves take 30 seconds.
Come to find out, the other guys were saving 1/4 res screen caps (the toaster saved two interlaced pages for a screen cap and averaged them together in the standard mode, saved 1/2 of one of the interlaced images if the fast mode.
Guy got all upset that I'd lied to him to make the sale, didn't know what I was talking about etc... Basically insisted I remove teh accelrator and refund his money.
I did.
Two weeks later he called to apologize for being such an ahole and asked me if I'd reinstall the accelerator (he'd gotten used to it in the two or three days it had been in the machine.) I charged him full labor costs for both the original install / deinstall and reinstall.