This isn't about Flat rate or about price gouging.

There are Forums full of people that have called tradesmen after hours and then later whine about how they think they have been wronged, why this is I'm not sure.

Fine, if you think you can do better, be my guest, I'd like my evenings to myself as well as my weekends.
Actually, I think that price was far too low, given the customer.

If they knew the pressure switch cost that much, why did they not go out and buy one and fit it, oh sorry I forgot, they lack manual skills.

Tradesmen are hired for (get this)their expertise not their time, when idiots that hire them realise this, the better off we will all be.

I like the "8pm Friday night and we had guests coming" bit, well maybe the plumber did as well.