If a customer approached me with their low low prices from another company, i would in turn ask the customer if they were presented with insurance, workmans comp, certification, and make the customer question "Just why is it that his prices are so low?"
Along with that being said, make sure to give your potential customers a copy of your insurance, workmans comp. and certification and references with pictures. It shows them you will be around next month when they have questions as the low baller has hit the bank and then ran to the hills....

just wait he wont be around long just think how long would you last if you charged half as much probably not long at all guys like this will come and go just make sure the customer understands that as well most people will pay more for professional company long before they let some nobody up on there expensive roof 

go behind him and his work and take pix of the damages and about 18 mo later take pix of the roof getting dirty already. Do a page in your sales book on him. exploit his weaknesses, insurance, chemicals, ticked customers, etc.

Then as he is going out of business offer him pennies on the dollar for his stuff.

Awe heck thats too much work..............................just go fishin!