My 2 cents:
Think the plumber in mention should have said ," It's $50 an hour for the helper" .Let them know the cost,that way it is easier for a person to get there mind wrapped around a price .
This "Flat Rate" thing can work well for us plumbers SOMETIMES . Like rugged said , If it had been $95 flat rate to open the drain and then the nightmare happens,,,you'd be screwed . I like to give a flat rate on a lot of things i.e: Ballcock replace , faucet cartridge replace , disposal . But TOO MANY THINGS can have unseen problems .I think it is SO important to build a relationship (professional) with your customers thatwhen these things happen they have come to trust and depend on us.Hey,if I've got to charge Mr/Mrs Smith and xtra $150 for unseen problems,they are going to be ok with that because they know that when they call at 9p.m. on a Sunday night with a waterfall in the living room ceiling,,,i'm on my way.
Bad enough the media has potrayed Plumbers Butt crack showing , Beer guziling , Money mongers,,,,,,Why give them more fuel for fodder ?
Be honest , " Look,this is the cost that I expect it to be, We very well may run into some unseen problems, Sorry but that will be additional.I can NOT say at this time how much,I will do my best to keep the cost down especially because we want to keep you as a customer and we would like you to refer us to your friends/neighbors."
Works everytime. Just tell the truth,then you don't have to remember everything.
Sorry for the speech
Cal