Yesterday I ripped out an old vanity unit and replaced it with a customer-supplied new one. I had to assemble the unit from a flat-pack, tailor it to fit, kit it out with the supplied brassware, re-route the supplies and waste, then seal in the inset basin.
The customer had been recommended me by a neighbour I had done some work for over a year ago. She had asked me for an estimate for the work, and I reckoned from past experience it would take the best part of a day (8 hours) to do it properly. So I applied my £45 per hour rate and quoted her 8 x 45 = £360 maximum, plus some materials (around £20 guessed). She was happy with this and asked me to go ahead.
In the event it took me 7 hrs 20 mins (and several cups of coffee) so I charged her £330 labour plus £29 materials (isol. valves, trap, sealants, new pipework and fittings, and some new waste pipes and fittings). This was below the original estimate.
She and her family were delighted with the end result - I have to say it did look good! - and paid up with no problem. Everyone was happy, including me!
The point I am making is that if you are recommended, and do a good job, and present a friendly and professional manner to your customers, and keep your word, you can charge much more than the £200 'day rate'.