I hate to say that 99% of those are scams.  I always recommend to people that they set up a separate wedding email and not give out your phone number to random vendors at the shows because a lot of those people will continue to call you non stop and promise you things that aren't actually free.  Some of them will even sell your information to other sketchy vendors.

I guess it doesn't hurt to listen to them, but be prepared for a hard press sales pitch.  If they tell you you have to pay any money at all, don't go for it.  Most likely they will tell you there are fees or that you have to sit through some informational session like a timeshare which lasts all day.  They are miserable and completely uncomfortable.  When a company calls lots and lots of people offering a free week long vacation, be skeptical.  If a legit company did that, they would make no money.  Usually, there's a big monitary catch to those deals.