There is always a catch when it comes to the prize. Remember that the prize is an end to a means. It is the bait to lure you to the presentation. You are always told that you have one of the following rather a specific prize. The reason that they do this is to get you to think that you stand a chance to win one of the big prizes while the odds are stacked against everyone attending that they will each get a complimentary prize with little value (and almost certainly with some cost to redeeming it). THERE'S NO SUCH THING AS A FREE LUNCH.
If you are promised a prize then get them to promise in writing that you have won a specific prize (get the marketer to name the prize and its value) without the obligation of buying anything!
Check out this soundbite about a couple in Durban who were conned into thinking that they had won a prize. This was featured on East Coast Radio's CONSUMERWATCH: