equioment and crew times, difficulty, extraction and cleanup.
The last can be a killer, the deadwood from a green ash or honey locust can double or tripple the raking compared to a similar sized silver maple.
Lastly, how bad do you want/need the work. Sometimes slaping a kicker on PITA work will pay off, if you get it. It's happened to me a few times. Work I did not really want, but dsiplayed myself as the msot professional to the the prospective client. Then I can bring in extra help/equipment and not worry.
Some jobs just need 10 manual labor types who want to work hard (read Latino imigrant, cannot find many white boys who want to do it) to haul chunks of wood out by hand.
One job had a 26 inch opening between the side of the house and a 6x6 fence/arbor post. A carpenter said it would cost $1000 to remove/replace it. Only way into the back yard.
Then you have those people anal about the lawn, and you price in cut and carry all debris with lawn repair.
On the simple stuff, which you would do it's all about what you need to make a profit.