Welcome to the forum,
This question gets asked a lot,
I charge more than most but I have the gift of the gab and people tend to want to pay me more... a lot of it is perceived value I explain more and quoting for a job I will prob spend twice as long with the customer talking and generally making them feel at ease about me being in their house.
I also explain that there will be blemishes ect and that the trowel is not a wand ect and most completely understand this and LIKE the honesty.... another point to me.
I also explain that I am exceptionally busy and that it will be a good 3 weeks ish before I will be able to make a start, once again busy = good.
If I have no work I dont say yes I can do that tomorrow I say leave it with me I maybe able to juggle some jobs around and fit you in.
When they say how much will it be my response is I dont like pricing on the spot as mistakes can easily be made can I call you tomorrow? if they are persistant I say off the top of my head you are looking at ...... (double the first figure you are thinking of) and see their reaction, most will say that is fine but still go away draw up a quote post it to them if it does work out more then put it in ect.
So back to the question, see how long it would take you, if it takes a day and you want/need Â£200 a day charge that plus materials.
I prefer to post the quote as 1 this looks more pro, and 2 means you can explain more about what is done and it can look like a lot on paper.... people like value for money.
If you phone them and say its Â£600 say it as if its only a small amount with no hesitation straight out and this works a treat.
let your confidence out!!
If they ask how long have you been doing it dont lie, just say a few years now, or christ let me think...lol
OK I have written enough now, some people may not approve of my methods but its what works for me.
PS hope all that makes sense