I hate giving serious advice.
If you're booked out two months ahead, I wouldn't worry about one or two customers cancelling. They would probably have been hard to work for anyway. I think it's all about attitude. When I'm really busy, I just get cockier. People sense it. There are so many great lines, and you feel like josey wales every time you get to use one of them.
"We're booked out till June. Most quality tree companies are the same. Of course, if you're not worried about insurance or property damage there are plenty of guys out there who can come today"
etc etc....
I once had a real rich snooty housewife giving me a hard time, looking down her nose at me while I was working in her neighbors yard and generally making my life miserable. She asked for a quote on some of her own trees, and I've never been happier to quote a job. Nothing like screwing someone while you've got a smile on your face
Casually I replied;
"sure, I'll be happy to come quote your trees. The price may be a little out of your budget though."
That sure riled her up good! She went to great lengths to insist that it was well within her means and that money was no object. So I figured a high price, trippled it, then added a little more and rounded it up for good measure. Plus sales tax. The look on her face when I told her the price said it all. While she was thinking about it, I had to offer her some consolation;
"Of course, not everyone can afford quality tree care. You may like to get some other quotes and look for something a little more affordable"
She had to choose between letting me politely insult her, or letting me rip her off. Either way, win win for me
Shaun