It does make me laugh, and yes it is often interfering relatives.
I have one customer that is ok, but the house is a right pain as getting onto the driveway is awkward being it's on a bend and up a hill. Customer herself is fine though, been doing this for over 3 years.
Anyway, one day I turn up and there I am cleaning away, and the customer's mother turns up while I'm halfway through. I finish up, start packing up the van and the mother comes running out saying I can't be finished because the windows are still wet and it's been too quick. I politely explain that the windows will dry no problem as the water is very pure etc etc. Didn't even acknowledge the 'you've been too quick' comment as I was already half-way through when she arrived.
So at this point, she is dancing along the edge of getting dropped, and in my head I think if she doesn't just say "ok" and walk away then that will be it (which is a shame for the customer who did nothing wrong, but I wouldn't be sad to drop it because of the awkward driveway.)
Amazingly she said "ok" and walked away, narrowly avoiding losing me. However, a few days later, customer emails me asking to go to every other month (from monthly), almost certainly because of the complaining interfering mother. I agree, now thinking I should just drop it, but instead decide to put the price up by £5 (house is £16) thinking she is bound to say "no thanks."
She says "ok"
So the interfering mother simply cost her daughter money.
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Another time, a house I'd being doing for about a year, one day the bloke happened to be in (instead of the wife who originally called me). He came out while I was there asked how much I was charging. I told him and his face turned a strange twisted shape, and he said "I think we'll leave it from now on". I just said ok no problem, finished the house and started packing up.
Just about to write the card out and I hear the lady shouting at him from inside the house. Then the lady comes out and says (in his earshot) "ignore that stupid puff, he hasn't got a clue, just carry on as you are". I tried not to laugh at her calling him a puff and just agreed.