Well John - you obviously aren't doing all your first cleans to a very high standard if they only take five minutes extra. And I hope this post helps the unbiased reader.
However let's assume that your generalisation is true and you are taking five minutes extra.
Let's also take just one of those "3 bed semi's" you mockingly use to illustrate your post at my expense.
A repeat clean 3 bed semi (with two 3 facet bay windows and a bedroom window and a door at the front, a side window and a door plus four windows at the back including a patio door set. Let's say that takes 15 minutes on 4 weekly and 18 minutes on 8 weekly. (typically extra spiders' nests or baked on bird muck and going above the vents from time to time raises the average time on the latter.)
If your extra 5 minutes to clean it is correct then you spend 33% extra time cleaning it. Therefore you can justify charging say £20 instead of £15.
Personally a first clean done thoroughly on my above example would probably take me 25 or 30 minutes because I would want all the spiders nests and filth above the vents got rid of and so I would scrub the whole property top to bottom quickly and thoroughly including the cills and then I would go back to the first top window I did and then go back over the glass.
I would then do the downstairs glass starting with any window not being dripped on from above and then the rest in reverse order.
I happily invest a bit extra in a first clean and charge accordingly. Because unlike you I'm not rushing it in "5 minutes extra" I have time to let it drip without driving back to finish off the glass.
I would charge £25 for a first clean (more or less depending on how filthy it was) and offer 8 weekly at £15/16 or 4 weekly at £13/14.
Then I know I have protected myself against one hit wonders masquerading as regulars.
You see thats where we differ I would take 30 mins on first and repeat cleans.
Im always amazed by guys who rattle round a house in 15 mins who believe that they are protecting
themselves against the competition.
So every clean is approached as though it hasn't been cleaned in years, even if cleaned 4 weeks ago? I must have that wrong because it makes little or no sense.
Its not what im saying.
I find that I can do first cleans every bit as quick as a repeat, maybe Im being too fussy with my
repeat cleans.
Another reason is that I only put water above vents when doing very dirty first cleans.
Which I then leave and come back later that day to finish the glass.
On repeat cleans I use a damp microfiber on a harris pole with a fixi clamp above the vents
this would be slower than using water.
At the end of the day I have priced to take 30 mins so I would rather over clean and work
at a calmer and less stressful pace.