When you book online, you're often on your own.

That's the message we hear again and again from fellow travelers: When that room that looked great online turned out to be a dump; when you forgot and booked the rental car in your maiden name; when you booked a tour at a euro price when you thought it was dollars -- you've got no one to blame except yourself.

Linda Smith of Miami heeds that lesson. Though she's never been burned booking online, she's cautious. So when she found an unusually good deal for a New York hotel room next March at an unfamiliar booking site, she snagged it. But she contacted us to find out how to vet the validity of an Internet site.

A savvy consumer, Smith already had done what she could.

She carefully checked the booking rules, which allowed her to cancel without penalty until the day before check in -- a more liberal policy than what's allowed by some sites.

She checked for professional memberships: The site claimed membership in organizations including ASTA (the American Society of Travel Agents), though because the company does business under several names she had trouble verifying the membership.

She checked with the Manhattan Better Business Bureau and found out that the company has a satisfactory rating.

She called the hotel and verified that they have her reservation. And she talked with her credit card company, which told her they would offer a credit if the room didn't exist at the last minute -- even though the charge was initially made months earlier. (This isn't the case with all credit cards.)

''It's a terrible feeling -- you could be in New York without a place to lay your head. Online, you don't know who you're dealing with,'' she says. ``I won't know until March how it worked out.''

Is the hassle worth it? For Smith, the answer is yes. The savings was more than $125 per night.

About 29 percent of other leisure travelers agree. That's the percent who booked last year via the Internet, for total sales of $86 billion, says Henry Harteveldt, vice president at Forrester Research, a firm that closely tracks travel trends.

But the Web isn't just about saving money. For the past decade, travelers have been able to research global trips, trade tips with other travelers and evaluate options easily -- at whatever time of day or night they like.

Increasing, technology is helping them do it more easily. Some sites -- usually those set up by an airline or hotel -- offer ''talk back'' options where you can speak with an agent in real time via the Internet.

Many have added e-mail newsletters and downloadable widgets that alert travelers about sales and price changes on trips that interest them most. On some sites, for instance, ''you can say, here's my budget, and they'll let you know when a fare that meets your budget is available,'' says Harteveldt.

TRAVELER REVIEWS

One of the biggest additions of recent years: Traveler reviews.

Since launching in 2000, Trip Advisor has racked up more than 10 million hotel reviews from 5 million registered members. With more than 25 million unique monthly visitors, Trip Advisor rates as the world's largest travel community, says spokesman Brooke Ferencsik. Though hotel reviews are the site's best known feature, user-generated photos, videos and ''go lists'' -- individual travelers' favorites -- are growing.

The drawback: At Trip Advisor, anyone can post a review, whether they've stayed at the hotel or not -- and whether they're an experience traveler or a novice.