There's a fine line between informing and being a know-it-all. The best approach in overcoming objections is to be prepared with a quick answer -- not a pamphlet from the Pink Panther that you retrieve from the glove box or email to them two days later. Remember, people Want To Buy, they don't Want To Be Sold. Educating the customer is easy -- the hard part is making them think they came up with the solution. Its called "Leading Them Across The Bridge" and its tough.
Mr. Customer:
Can we research your options here on my fancy iPhone?
Did the roofer provide a reason why sodium hypochlorite is the wrong product to use on your roof?
Did the roofer provide you with any options -- other than Not using sH? Did he suggest a new roof instead?
Did you know shingles are basically asphalt with grit applied to it?
Can I provide you with the names of several customers that have benefited from our treatment?
If I could clean your roof for $500 instead of new shingles for $15,000, would that a benefit to you?
Hell, you might even play dumb and say, "Wow, Mr. Customer, I didn't know that bleach could hurt shingles and it appears that I may have damaged several roofs last summer. What should I use instead?" That is the hardest to pull off.
Most objections are easily overcome, prep is the key. It all comes back to having an Elevator Pitch and knowing your Service in/out. Its kinda like liberals, once you isolate each of their "objections" and probe with appropriate questions and/or provide info, it usually ends with "Bush sucks!", or, in this case, "I'm not putting bleach on my roof because a new roof costs as much as a new car". Your job is to explain why NOT cleaning the roof may accelerate the wear on the current one. And if you do it right, you have a customer for life because they realize that you: a) didn't try to sell them more than needed; b) you were "looking out for them", and; c) you weren't condescending in the process.
Encourage the customer to call a competitor or roof supply or whatever. Again, the key is to help the prospect discover the info and then make their own decision. No one likes to be told that they are wrong.
