A lot depends on the specific company. Saying all insurance companies are alike is no more correct than saying all contractors are alike. Some firms are pretty straightforward, while others are crooks.
Best advice is to be fair and be honest. Charge them as your would anyone, and make sure that you and they fully understand the scope of the work to be done. The only caution is to take extra pains to document the job - before, during, and after.
If you're going to have trouble, it will most likely come from the customer, rather than the insurance company. I've had a few want me to give them my bill for them to 'forward' ... when their real intent was to mark up my bill and make themselves a 'commission.' Such antics WILL complicate things.
These days, I would assume a 90-day pay for any customer that's "corporate." Again, this will vary by firm. Some like to play games, while others don't.
"Research" the firm. That is, ask them for names of previous contractors - and ask them. Ask your insurance agent, your lawyer, your bank for any information they might have on the firm.
The usual warning signs apply: if they make a fuss over how 'big' they are, or how 'legitimate' thay are ... take warning. Be aware that similar-sounding names may have absolutely nothing to do with each other (ie: Hartford Life and Hartford Steam Boiler).