RIFT: play for free - but there's a catch

I've had an email from Trion inviting me to play Rift for free from August 25-31. Very nice of them and I'll certainly take them up on the offer.

Bizarrely though the small print includes this detail:
If user subscribes to RIFT during free gameplay time, user’s credit card or pre-paid game time card will be charged immediately, and any remaining free gameplay time will be forfeited.

Heaven forfend anyone pay them money!