as Paul said, it depends which part of the country your in.
Also i have found if you get too ambitious you'll lose jobs.
Most people just want a clean and want you in and out.
I dont use weed killer as my machine just cuts through them.
The method I use, I dont even need to use a patio cleaner, but i do use a cheap detergent that creates bubbles as they do like to see this.
Re sanding I price from 30 quid depending on the size of the area.
Sealing, I dont do it, I dont offer it.
If they want it doing I put them on to my concrete guy who is a pro in this field.
But I do recommend that the areas do need cleaning twice a year and if they sign up to this they get a discount, plus they are then in next years diary, this way you are not chasing work the following year.
The best advice I can give is.
Be and look professional at all times.
Never rush.
Always throw in a little freebie, like cleaning in or around a drain or the odd gate post.
Work to the highest possible standards.
Always walk customers around the job after you have finished and make sure they are completely satisfied before any money changes hands.
This way makes them feel like they are important (which they are).
Then they will recommend you if they hear of someone wanting some work doing.
Most of my jobs come in by the way of personal recommendation.
Top Of the list.. Get insurance.