No harm in attending I suppose, as long as you ain't travelling hundreds of miles for it and you don't take your credit card..
The problem is that, for many people, there is harm in attending. I am not suggesting it is the case with you because you rightly point out don't take your credit card.
These so-called "free courses" are merely selling opportunities. They are designed to draw people in using the same psychological tricks as have been used to sell time-shares and other get-rich quick schemes. The salesmen are often slick and present promising lifestyles. The language used is chosen carefully. There will always be some bait to get you to buy immediately "we like you guys, you have turned up tonight and so you are entitled to a special discount, if you buy now etc". The session will often be high-pressured and very intense. They know that if you leave without buying then you will have time to reflect and probably come to your senses.
They might well offer some tit-bit of "useful" information to the newbie, but these tit-bits are so easily obtained here and elsewhere both free and devoid of psychological pressure.
I sincerely hope that Timsk will add some advice to his "Essentials" thread to be very wary of all of these schemes and their free introductions highlighting the psychological tricks they use.
Charlton