Why didnt you view the job ?
im doing a large conny roof clean in the morning , the customer described this as being slightly green . Wasnt slightly green when i went to LOOK .
Allways view the work before any price is agreed , try to do the the worrk on the day you quote if the customer is happy with the price .
If you can not do the job that day but have been accepted to do the work , tell the customer you need to pre-spray the conny with a detergent (usually fairy watered down) , charge a deposit for this EVEN if only a few quid , less likely the customer will back out .
As for ecover never used it