A tree service should carry BOTH full liability insurance and worker comp insurance. Make sure to have the Company's insurance agent fax or e-mail it to you directly. Don't accept a copy handed to you - it may be out dated or have a change in coverage. Don't hesitate on this, it is the standard for all industries to have the agent or insurance company send it to you directly.
Often, company's with provide one once you sign the contract, with the condition that is becomes binding when you receive all the proper paper work. We adopted this policy when every who got an estimate wanted a copy. Our Insurance agent was going insane. Only ask it it be faxed to you when you are at a serious point of making your final decision.
Be careful of landscape companies that do tree removal, there insurance code - extent of liability and amount of coverage - differs vastly from a reputable tree company. Things go wrong eventually (Nothing is 100% fool proof, especially with mother nature) and you want to make sure you have coverage for large tree removal near buildings pools and such. If a new patio, pool . . . is seriously damaged by a landscaper, your homeowners pollicy might have to contribute to get expensive things properly fixed.
Madden Tree, Inc