Data selling from big tech companies is the least of your worries tbh. It's all presented in aggregate form and protected very well. It isn't even really data selling, although if you want to argue semantics and model it as such, it would be data selling limited in scope in that the only action an advertiser can use the data for is presenting you with an ad.
It's the financial industry that you have to worry about. The finance industry has atrocious security and access to very personal information on you. Finance companies (your bank, credit card, etc.) sell your information to the highest bargainer with much higher privileges (physical mail and junk emails) and don't allow you to opt out.
Edit: And also the health care industry. Super personal information with archaic tech and paper thin security. Data might not be sold but the risk of bad parties gaining access to your information is high.
It's the financial industry that you have to worry about. The finance industry has atrocious security and access to very personal information on you. Finance companies (your bank, credit card, etc.) sell your information to the highest bargainer with much higher privileges (physical mail and junk emails) and don't allow you to opt out.
Edit: And also the health care industry. Super personal information with archaic tech and paper thin security. Data might not be sold but the risk of bad parties gaining access to your information is high.