Be a sleuth

If the name of the company is in the listing (most are), you should be able to locate a website, phone number, and address with a couple of online searches. If there's no trace of the company, think twice about proceeding.

Bids via LuxuryLink for a six-nigh package at Belize's Jaguar Reef started at about half the retail price [enlarge photo] MARCH 2006 ISSUE • Table of Contents • Dream Trips: 2006 Edition • The Hungry Man's Tokyo • 50 All-Star Family Camps • Trip Coach: The Caribbean • Road Trip: The Northern Neck, Virginia • 40 Best Vacations

Look for PayPal

Be doubly suspicious of eBay sellers that don't take PayPal, which allows you to use your credit card or checking account without sharing either number with the seller.

Read the fine print--twice!

At the minimum, expect blackout dates and penalties for changes (or no changes allowed). And look out for fees. Luxury-Link charges $20 for every purchase, and there are sometimes additional fees--at one Honduran resort, a 10 percent service charge is assessed at checkout. SkyAuction tacks on $32 per night at hotels and $195 per week on many condos.

Ask questions

Specifically, ask if the dates you want are available. This may be difficult. LuxuryLink lists a toll-free number on its website (888/297-3299) but refuses to confirm availability. SkyAuction only gives out its number to customers after they've won an auction. ("If we had to do customer service by telephone for every prospective bidder," says CEO Michael Hering, "we wouldn't be able to operate.") EBay customers can click on "ask seller" to send confidential e-mails. If you have little or no flexibility and can't confirm dates, pass.

Observe and learn

Sellers post the same packages over and over. Watch how a few auctions proceed before bidding. Be ready for a fury of bids at the wire. "The last half hour is when 50 percent of bids come in," says Hering.

Don't "buy it now"

All three sites allow customers to make certain purchases on the spot. They're rarely a good deal. One Luxury-Link package included breakfast and lodging for two at the Nine Zero hotel in Boston for $249 (plus taxes and its $20 handling fee); at the same time, the hotel posted a $239 promotional rate for lodging only (no breakfast, but no handling fee either).

Bid at your own risk

Many travel companies prohibit selling vouchers, discount coupons, rewards points, and frequent-flier miles. EBay rarely stops sales of such products, but it has revealed sellers' identities in the past. "I've gotten registered mail from Starwood warning me that they'd shut my account down," says one user outed by eBay for selling Starwood vouchers. Still, when we last checked, Southwest Rapid Rewards tickets were going for $275-$350, even though the airline deems them "void if sold, purchased, brokered, or bartered." If you are busted, the airline can freeze or delete your frequent-flier account, as well as refuse to honor the ticket.

Monitor your bid

You'll be alerted via e-mail if someone outbids you, and then it's decision time. Don't get carried away. Decide in advance on the maximum you'll spend, and stick to it.

Beware the bait-and-switch

After winning a Cancún lodging package at SkyAuction, Erik Staley, of Carlsbad, Calif., discovered that what he bought was different than what was listed. SkyAuction was actually selling a room in the Oasis Cancún, not the Grand Oasis advertised--they're both parts of the same resort, but guests at the former have smaller rooms and less amenities. Staley got a full refund.