Unlike most products, travel services usually have to be paid for before they are delivered. This creates opportunities for disreputable individuals and companies. Some travel packages turn out to be very different from what was presented or what the consumer expected. Some don't materialize at all! If you receive an offer by phone or mail for a free or extremely low-priced vacation trip to a popular destination (often Hawaii or Florida), there are a few things you should look for:

* Does the price seem too good to be true? If so, it probably is.

* Are you asked to give your credit card number over the phone?

* Are you pressured to make an immediate decision?

* Is the carrier simply identified as "a major airline," or does the representative offer a collection of airlines without being able to say which one you will be on?

* Is the representative unable or unwilling to give you a street address for the company?

* Are you told you can't leave for at least two months? (The deadline for disputing a credit card charge is 60 days, and most scam artists know this.)

If you encounter any of these symptoms, proceed cautiously. Ask for written information to be sent to you; any legitimate travel company will be happy to oblige. If they don't have a brochure, ask for a day or two to think it over; most bona fide deals that are good today will still be good two days from now. If they say no to both requests, this probably isn't the trip for you. Some other advice:

* If you are told that you've won a free vacation, ask if you have to buy something else in order to get it. Some packages have promoted free air fare, as long as you buy expensive hotel arrangements. Others include a free hotel stay, but no air fare.

* If you are seriously considering the vacation offer and are confident you have established the full price you will pay, compare the offer to what you might obtain elsewhere. Frequently, the appeal of free air fare or free accommodations disguises the fact that the total price is still higher than that of a regular package tour.

* Get a confirmed departure date, in writing, before you pay anything. Eye skeptically any promises that an acceptable date will be arranged later. If the package involves standby or waitlist travel, or a reservation that can only be provided much later, ask if your payment is refundable if you want to cancel, and don't pay any money you can't afford to lose.

* If the destination is a beach resort, ask the seller how far the hotel is from the beach. Then ask the hotel.

* Determine the complete cost of the trip in dollars, including all service charges, taxes, processing fees, etc.

* If you decide to buy the trip after checking it out, paying by credit card gives you certain legal rights to pursue a chargeback (credit) if promised services aren't delivered.

For further advice, see "Other Sources of Information" at the end of this brochure for details on how to order the Federal Trade Commission's pamphlet Telemarketing Travel Fraud.