There is a "critical mass" of user engagement that a brand or person has to have to get included in the suggested results. I believe you can just type in whatever you want, but I find the best results occur when the audience has at least 250,000 people in it (But less than 2,000,000). That will be hard if you just type in a low engagement target. I get a lot of cross sell with a fairly popular author, a guy who sells A LOT of books. But his Facebook presence still isn't big enough to generate a decent target, and his name does not generate a suggested target in Ads Manager.
From an advertising perspective, this is not a problem. His 5,000 followers are not worth the cost of impressions. Not because they aren't potential customers, but because the money used to target them would be better spent reaching out to a wider group. Funny you mention Stephenson, because I absolutely target people who like him. I buy impressions from HIS customers because there are more of them and they are accustomed to paying more for books. I like customers who aren't afraid to spend real money on books. The ad spend goes to more people who are willing to spend more money. I spend a lot of time on David Weber's audience, as well as John Ringo's.
Truthfully, you will have better results if you hitch your audience to higher-engagement brands.
Also, where do your ads point the customer?
