I could be wrong on this, but I am pretty sure, under british law at least (am I putting enough qualifiers in this yet?) that they have to atleast give you the option of opting out of giving them the right to sell your details, just saying if you join you give us the right is illegal. Comes under the data protection act. I am pretty sure most other countries have similar laws. So if they haven't given you that option, and they do sell your details, they are possibly breaking the law.