I've done it a few times, and a few times read, or started to read, the free book I got. I can't remember liking any of them well enough to buy more books from the author, though.
On the other hand, there are at least five authors I've discovered by reading fan fiction they wrote and shared for free, and who I've bought two or more books from.
I get several author newsletters that mostly stay unread in a folder, and which I probably should unsubscribe from. The ones I read are by favourite authors. Courtney Milan has one that's
mostly about tea 