Not sure on Craig's List....
Craig's List is a bit tricky - it is free advertising, but it is free for every clown in the city with a chainsaw and pickup truck...
To me, there are two types of people on CL - people who like to use small, local business and then the 'garage salers' - those who think everything in the world should be offered with a discount. My advice would be to use CL sparingly and selectively...
Today, I talk to a potential CL customer about the removal of a70' pine in the backyard (wires / utilities and fence, a lowering job, no floppin'.) She was trying to 'beat the other estimate she got.' I'm thinking another offer is $1400 - $1700, so my $850 bid for the removal should have me back on her property in a couple of weeks. She sarcastically states that she should call the other guy back and his $320 bid. I told her if he has the insurance, I would do it (call him back) in a heartbeat, and good luck, etc....
I agree with contacting tree companies. Other than that, be on time, act professional, and don't leave a mess and word of mouth will keep you busy in no time at all...