Though only 13, Sarah Thurston of Cape Elizabeth is serious about her tennis.

She had set her sights on a new racquet. Not just any racquet, but a braided graphite and Kevlar Slazenger Pro X1 weighing a slight 12 ounces, sporting a 95-square-inch head and 27-inch length, with 8 points head light and a 16/18 string pattern. Don’t ask what that all means. But that’s exactly the racquet Sarah wanted to suit her height (5-foot-2), arm length and strength.

Now, Sarah is one of those special people who doesn’t expect Mom and Dad to pay for everything. She spent the winter baby-sitting and saving soda bottles to buy the coveted racquet and a new tennis outfit. By February, Sarah had saved more than $200 and started shopping online.

Slazenger Pro X1 racquets usually retail for $149, but Sarah, a smart shopper, discovered a “special bargain price” of $129 at Top Sports Ltd. in Burbank, Calif. Using Dad’s credit card (with permission), she ordered the racquet and a Balle de Match girl’s sunshine top and cloudy skirt for $26.99 each.

Two weeks later, UPS dropped off a package from California while Sarah paced nervously inside the house. According to her mom, Sarah “wore a rut in the rug” during the wait. She was in her new outfit almost before the packing box hit the floor and, before long, she was practicing her backhand in the living room while Mom watched the lamps and chewed her fingernails.

The only thing keeping Sarah from her destiny at Wimbledon was the 16 inches of snow on the ground.

But surely as McEnroe will bark at a line judge, Maine’s snow will melt. And once the puddles were off the courts and the net was up, Sarah was out there on her schoolyard court.

She hauled her little brother Timmy along as a practice dummy.

But the first time Sarah tossed her Wilson titanium tennis ball into the air, it came down hard with a crushing right-handed service.

Something felt terribly wrong.

Instead of a “boing,” she heard a “fump” (don’t ask … it’s a tennis thing). Her service came flying back, something Timmy seldom accomplished. But when she took her next slice at the ball: “fump.” The racquet was dead! There was no “sweet spot.” Every racquet has three “sweet spots.” In a general sense, the sweet spot is the area of the string bed that produces the best combination of feel or power or … the boing.

It was obvious that Sarah had received defective merchandise. She was crushed.

Then she talked to her dad.

Dad Thurston, who at one time had attended law school, counseled his daughter that surely the company would send a replacement. They were soon to find out what many Internet shoppers already know: There is nothing certain about doing business on the Internet.

Next week we’ll tell you the rest of Sarah’s story.

Consumer Forum is a collaboration of the Bangor Daily News and Northeast COMBAT-Maine Center for the Public Interest, Maine’s membership-funded nonprofit consumer organization. Individual membership costs $25; business rates start at $125 (0-10 employees). For help and information write: Consumer Forum, Bangor Daily News, P.O. Box 1329, Bangor 04402-1329.