It's easy to think that trees are among the few great things in life that are free. They increase our property values, provide shade, create autumn scenery, and help create the air we breathe.

But sometimes, there may be a price. To keep your trees healthy or to get rid of dying ones, you may want the benefit of professional advice, skill, and labor.

To help you find this help, nonprofit consumer group Delaware Valley Consumers' Checkbook magazine and Checkbook.org surveyed members and Consumer Reports subscribers about their experiences with area tree-care services.

Through Sept. 30, Checkbook is offering free access to its ratings of tree-care services to Inquirer readers through this link: www.checkbook.org/inquirer/tree-care.

You don't have to be an expert to spot many potential tree problems. Examine your trees several times a year for the following:

Discolored leaves and thinning in the tree's crown.

Roots pulled loose from the ground and fungal growths on roots and main trunk.

Dead or fallen branches more than two inches in diameter.

Deep vertical cracks on opposite sides of the main trunk.

Sawdust on the trunk from wood-boring insects.

A trunk that noticeably leans in one direction and a branch canopy that is not roughly balanced.

Other unusual deformations and deposits on leaves, limbs, or bark.

Other reasons for tree work include eliminating the risk to your house or to electrical or other utility wires from rubbing limbs or precarious overhanging limbs; letting light and breezes more readily reach your house, garden or lawn; and protecting foundations and drainage systems from invading roots.

In many cases, the problem and the solution will be obvious: removing specific limbs, for example. But sometimes diagnosing and treatment are as difficult for trees as they can be with humans. At those times, you need expert advice. But don't assume that all estimators from tree-care companies can determine what's wrong and prescribe the correct treatment.

Checkbook's evaluation of local tree-care services found big company-to-company differences in the quality of advice and work performed. The good news is that many area companies were rated quite high for the quality of their work. But the news is not all good. Some companies received favorable ratings from only 60 percent or less of their surveyed customers.

Common consumer complaints included charging more than promised, producing bad results, and even property damage caused by careless or untrained workers.

If you need tree-care work, the best strategy is to get more than one opinion. Invite representatives from several companies to your home to offer estimates. Ask them to explain what they plan to do and why.

Along with several opinions, you'll get comparative pricing. Checkbook's undercover shoppers found big differences in prices for tree-care work. For example, for a tree-

removal job, companies quoted prices ranging from $1,850 to $3,930.

Typically, you don't have to be home when bidders are looking at the job, but do include a thorough description of the work in a written contract that specifies who cleans up afterward, hauls away debris and wood, and removes the stump.

What is not specified in writing is very unlikely to get done.

If a job can wait, consider having the work done in winter, when companies are less busy and there is less debris to haul away.

Also, check whether a company's liability insurance and workers compensation insurance are currently in effect. Ask to see certificates of insurance, and call the company's insurance carrier to verify. This is a serious concern because high-powered equipment, heavy branches and trunks, lofty heights, and proximity to power lines make tree work dangerous.

Finally, ask about the company's payment policy, to see how much of the total cost is payable upon completion of the job or later.

Paying after the work is completed gives you leverage to ensure that it's carried out properly and on time.

Delaware Valley Consumers' Checkbook magazine and Checkbook.org are a nonprofit organization whose mission is to help consumers get the best service and lowest prices. Checkbook is supported by consumers and takes no money from the service providers it evaluates. Access its ratings of area tree-care services free of charge until Sept. 30 at www.checkbook.org/inquirer/tree-care.