I have been cleaning drives for 10 years and working with paving sealers for nearly 20.
Applying sealer can be good for both your business and your customer, if a few simple guidelines are followed.
Manufacturers of the pavers Marshall's, Brett's etc would always say do not pressure wash block paving as it
1, Greatly accelerates the colour loss, surface wear and makes the blocks more porous, so susceptible to algae and lichen.
2, You increase the chance of dips and spreading as the sand underneath the blocks is gradually washed away.
With this in mind, my advice would be clean the drive properly once, then once dry, seal it properly using a good quality sealer in the right ratios. This means effectively flooding the joints on the 1st coat so that the sealer penetrates deep into the sand and sets the joints solid.
From then on a simple regular maintenance programme with occasional light wash down, with a top up coat of sealer applied every few years, should help keep the paving in great condition
There are various other do and dont's regarding cleaning and sealing paving, but a lot of it is common sense and can be learned quite quickly.
Hope this helps