there are thousands upon thousands of block paved driveways...you do not weedkill the week before...the pressure washer gets out weeds from roots up...you do not lift blocks...no need to do this.
If the blocks have sunk due to the layer not doing job properly/settlement whatever, you simply inform the owner of the fact.
You are there to clean the surface and joints...this is done so easily with pressure washer and flat surface cleaner.
When using lance, try and direct jet away from house...this is easily done.
Direct sand with your lance to a wall area away from drain and shovel up into a bucket.
After cleaning, and resanding, tell the owner to apply "pathclear" weedkiller to the area over the next week or so and repeat in 6 months and they should have weed free driveway for 12 months...then tell them to call you back to reclean.
I don`t even offer a sealing service...too many problems, too many return visits.
Keep it simple...clean, resand, drive away with money in your hand and your contact details in theirs.
I average 2-3 good jobs a week from advertising in local magazines @ £315 for 3 months in 4 magazines covering a population of 14000...those 14000 are the areas I want and they get my half page colour ad in their letter box every 4 weeks for 3 months...£315.00 all in.