Ian
On the form (software package) it has the space provided to put in a number on a scale. For the Actual age you put in the age (ask the client), for the previous cleaning you put in how many, for the level of soil you put in a figure between 1-3. The level of stain is again between 1-3, and finally for wear age a figure between 1-4. This then gives you a reading of whether they have light, normal or heavy soiling :

Not sure how you would calculate this in writing

The higher the figure the worst it is. For wear age 4 is excessively bad and 1 is hardly any.
It essentially pushes for protection and a maint plan. If your reading comes out at say 'extreme' soiling then it would need more than one clean/protect and because its harder to clean the price is higher. For 'normal soiling' conditions the price would be your normal clean & protect price.
I dont use the audit aspect anymore Ian as it all gets very time consuming. What with this, maybe a presentation and finally the quote - some clients feel that they are being sold to like a double glazing salesman!
I think a presentation can help in approx 50% of cases, others just want a price.
Kev