They are probably not dirt
Black patio spots are often lichen growing into the tiny pores of the paving. That makes them much harder to remove than loose dirt or the green film that builds up over winter.
Why more pressure is not the answer
Pressure washing can clean the paving around a black spot without removing the lichen itself. Turning the pressure up can damage the slab before it solves the problem.
The type of paving matters
Concrete, sandstone, limestone and porcelain all react differently. Any treatment also needs to be safe around plants, drains, pointing and old sealers.
What result can you expect?
Newer marks are usually easier to deal with than lichen that has been there for years. Some patios need a separate lichen treatment as well as a general clean.
Not sure about your own property?
If you are in Ryedale or nearby, send Will a couple of photos and a short description. He can usually tell you whether the surface needs a closer look before quoting.