Internet service providers have the power to collect a tremendous amount of metadata: your legal name, age, email, social media accounts, photos, residential address, and browsing history. They have the power to profile you based on a wide array of fingerprinting techniques. On most networks, anonymity is impossible.
There are many dangers that could result from an abuse of this data. Identity theft, online harassment, selling data to advertisers are just a few of the many possible abuses of private data.
gry's Proposal
Do not share data, with or without a reward, to 3rd parties. Three excuses to break this rule: