Did they find it by going to that site or did they get some sort of mailer or phone call about the deal? Often times the deals that people get by mail or over the phone involve paying some sort of "processing" fee up front and then they book their trip and it ends up being based on availability, or needs to be booked through their "partner" and in the end is more expensive than if they had booked themselves.

I don't know anything about the company in question, but think if the deal is truly 50% less than anything they've found elsewhere there might be reason to question things. If they're looking at spending $1,000+ per person they shouldn't have to settle for dates they really don't want. Not that they should get prime season for tha kind of money, but it's already a decent chunk of change and once they've committed that much they really should consider how much more it would be for dates they want.

Of course being a FT'er perhaps you have the miles they need for a flight so they can save on that end and use their money on the land portion.