Like I said, they probably mixed up their clients, as I am taking the client/commenter's explanation here at face value, but that doesn't make them scammers as some suggest they could be.
But if you leave cash, odds are, if they don't see it, they'll be informing you of that before you get to the car.
Unfortunately, Paypal puts the providers at risk as a bad client can reverse their payment once they're gone, and leave the provider totally screwed. They can duke it out via Paypal but obviously if details of the service aren't in concert with Paypal's terms, it gets murky and perhaps more costly.
There are scamming providers out there, but usually, thanks to a site like this, word of mouth spreads quickly about their lack of character. Given Froy & Gabrielsp have been around for some time, and have almost entirely stellar feedback, I think they deserve the benefit of the doubt as far as any scamming accusation is concerned.
There are bad clients too, and as I saw another provider shortly after this happened to him, I saw the hurt he felt that he was used like that, which, I suspect, felt worse than the loss of income for one session.