At Schwab, you have to sign a few documents and then they open a separate secures lending account tied to your main account. At the end of the month, your lending account is credited with the interest earned and then that amount is transferred into your main account. Lots of visible steps!! There is no back room shenanigans played at Schwab!
Frob, on TD Ameritrade Client Services - General there is an option to enable "fully paid lending income", I'm thinking you need to enable that feature before they lend your shares at interest
Schwab has borrowed from my IRA accounts under their program. Obviously, those are not margin accounts, but I did specifically have to enroll my IRAs in the program.