Homeowner guide
After a storm, a lot of strangers knock on a lot of doors. Here is how to tell who is real, in about ten minutes, without taking anybody's word for it.
The short version. Ask for the license number and check it with the state yourself. Ask for a certificate of insurance sent directly from their insurer. Never pay a large deposit up front. Never sign anything that lets a contractor deal with your insurance company on your behalf until you have read it twice. Everything below is the longer version of those four things.
Ten minutes
In Pennsylvania every home improvement contractor doing more than $5,000 a year has to register with the Attorney General, and the number starts PA. In New Jersey the number starts 13VH. Do not accept a number written on a business card as proof. Look it up on the state registry while they are standing there.
General liability and workers compensation. A PDF a contractor emails you can be anything. Ask for it to come directly from their insurance agent, which takes them one phone call and tells you a lot about whether they want you checking.
Then check the Better Business Bureau and Google reviews. Look at whether the reviews are spread over years or all appeared in one month, and whether anybody from the company answers the bad ones.
Most roofing companies use subcontracted install crews. That is normal and it is not a problem. What matters is whether they will say so plainly, and who stays responsible for the job when the crew leaves.
In Pennsylvania a contractor cannot collect more than one third of the contract price up front on a home improvement contract. Anybody asking for half in cash before materials are ordered is telling you something.
A contingency agreement or an assignment of benefits can hand a contractor the right to deal with your carrier and to keep the job even if you change your mind. That is not automatically bad, but it is not a work order and it should never be presented as a formality.

After a storm
When hail or high wind goes through a county, crews travel in from out of state and work the neighborhood for a few weeks. Some of them are good. Some of them will be unreachable by the time the roof leaks.
The pattern to watch for is urgency: a discount that expires today, an offer to cover your deductible, or a claim that they saw damage from the road. Covering a deductible is illegal in Pennsylvania, and anybody offering it is telling you how they do business generally.
There is nothing wrong with a company that came from somewhere else. The question is whether they will still exist in five years when a shingle lifts, and whether the warranty is with a manufacturer or just with them.
Warning signs
Straight answers
Any legitimate contractor gives it immediately and expects you to check it.
Condition One is PA168434 in Pennsylvania and 13VH11942300 in New Jersey, and both are published on every page of this site rather than produced on request.
Ask the company, not the person.
It is a fair question in storm season and any real company can answer it. On this site you can type a name into the crew page and check it before you let anybody in.
After, in almost every case.
You want to know whether there is documentable damage worth filing before you put a claim on your record. A free inspection tells you that, and an honest contractor will say when there is not enough damage to bother.
It survives the contractor going out of business, which is the entire point.
Manufacturer warranties like the GAF Golden Pledge require a certified installer, which is why certification is worth asking about rather than taking as marketing.
Pennsylvania gives you three business days to cancel most home improvement contracts signed at your home.
Put the cancellation in writing and keep a copy. If you are past that window it is worth a call to the Attorney General's Bureau of Consumer Protection.
License numbers published, crew you can look up by name, and a free inspection with photographs of whatever is up there.