You'd probably be surprised how many roofing crews aren't insured and bonded, which means if they fall off or get injured while working on your property, you're liable. Protect yourself by requiring proof of insurance.
Some roofing products offer kickbacks to contractors who push their supplies. Here's a thought: if your product is good, why should you have to pay me to sell it? Ask your contractor which products to avoid and why.
Is this contractor really a local company, or are they storm-chasers who picked up a cheap local number and won't be around to take your call when the roof starts to leak? Is that brand really as good as you're being told it is? Make it the responsibility of your contractor to explain their product to you, but then don't forget to check it out for yourself.