Best Buy's Black Magic Tracks My Stealth Purchase

Reader bethSmash is freaked out that Best Buy sent her a follow-up email even though she didn’t give the clerk her her address or even flash her loyalty program card when she bought a wireless router. She assumes the corporation connects her credit card number to her email address, which she must have given Best Buy when she signed up for the program, through some sort of privacy invasion trickery.

She writes:

I went to Best Buy the other day to get a wireless router (I know, I gave money to the enemy, but I didn’t have time to order online). I at one time signed up for their Rewards card but did not have it on me and did not give them my phone number, email address, or any other identifying information during this transaction. I did however pay by credit card and was forced to give them my driver’s license – the clerk told me that I was wrong about the merchant agreement and I was too tired to argue. I get home, think everything is fine, and then the email shows up. Does this mean that I am in the Best Buy system according to my credit card? Or did the little jerk behind the counter use my DL info (he didn’t swipe it). I’m definitely uncomfortable with them contacting me like this (and for GeekSquad to set up a wireless router?).

Any advice for how to protect myself from Best Buy’s all-knowingness?

Has Best Buy sent you follow-up messages in this manner?