The truth is, I don't know the answer to this question. But it's one that's been on my mind a lot lately.
As an author with two books about to be released next year, I think the line between self promotion and spam is getting fuzzier and fuzzier. In fact, I can't seem to go onto Facebook, Goodreads, Twitter, or even check my own email without getting bombarded by it. And, what I don't think some authors realize is that, when they bombard me with spam, not only does it annoy me greatly, but it makes me not want to buy their book purely out of spite.
Here's a list of my top offenders:
1. Inviting people to events through Goodreads and Facebook. While I hate these, I understand why authors feel the need to do it. If you're hosting an event, such as a book launch, you're going to want as many people to know about it as possible. But maybe a direct email to people in your area would be a better, more personable option. Chances are, if your launch is in Houston and I'm in St. Louis, I'm not going to show. In fact, if I see an email with "Event Invitation", honestly, I don't even read them--automatic delete.
2. Reposting tweets from a reviewer about how much they enjoyed your book. I can see why people do this. They're excited about the good review and they want to thank the reviewer publicly. But I'll be honest, I have NEVER clicked on one of these review links and read the review. Have you?