Roots from neighbors....legal issue

[Matt Smith]

I am in California. There is a tree on my neighbor's land that has roots coming on my land, lifting the soil and now dangerously going under my house. I got 2 quotes from arborist and asked my neighbor to send me the check payable to the cheapest quote. I informed him the tree might die and might fall when the roots are removed...and that he might just cut the tree as well. He answered that he doesn't have any money and want to cut the roots on my property himself. I am concerned. Can I let him do it? What if he doesn't do it well or injure himself? If he does it, should I have him sign some kind of waver, and that he is responsible if it is now done well and the roots damage my property? Should I accept or stick to a licensed contractor?