Roof wash tuition

I was doing a window job last week and saw that the client had just a couple of ugly areas of roof. Sold them on adding on a partial roof wash while I was there.
Turned out good, then got a call yesterday that the trim on the garage had bleached in spots. Went by today to check it out, did some test spots and could not recreate the problem, but it definitely looked like it was from me (forgot to take pictures of the problem).
Called the customer, turns out he had just painted the trim. $3 paint brush and 10 minutes of painting, customer satisfied and lesson learned. Now I know to watch for the good looking paint, I guess.
Any other glaring things I should look out for, other than vegetation?