you might think the guy is under charging but others would dis agree, why cut yourself short charging £12 less??
you run a business not a charity if someone is willing to pay £30 then you would be a fool to take less,
just think about it, if you was to underprice each customer on your round by £3, and you did 200 jobs each month then you are potentially losing six hundred pounds a month
no point in undercutting whatsoever