Re: wrong fuel
Surely it is the other way round? Petrol in a diesel will ignite early under compression and burn in an explosive manner, potentially causing serious engine damage. The only thing that would prevent that happening is if the fuel pump was unable to pump the petrol for some reason.
Diesel in a petrol however, the car would just get very smokey and grind to a halt. Still a time consuming job to clear the fuel system, and probably would damage lambda sensor and cat, but won't cause serious mechanical damage.
Either way - if you put the wrong fuel in and realise before you drive off, don't start the engine, just push it off the forecourt and get the tank drained - if you have to pay someone to flush through the whole fuel system it isn't going to be cheap!!