Richy,
dont think its plain sailing and there are no problems with commercial customers, compared to residential customers.
Infact it can go opposite way, they can seriously drag their feet in payments, and believe me if they owe you a fair bit you will drive yourself nuts if you havent got the funds available to cover waiting and waiting.
Also, another point is that some commercial can be very very big with lots of work, and if you dont cover the lot you can and will be dropped by them.
Health & Safety can be mega, not just risk assessments etc, but very very keen, even when you put everything into place.
I refuse quite abit of work for these reasons alone, and pick and choose what exactly i am looking for.