The folks who book the county fair each year at the Del Mar Fairgrounds usually announce the majority of headliners all at once, most of them free with admission. This year, they’re rolling out the announcements one by one, perhaps because next year’s slate seems to include more ticketed events than usual (though most concerts do match the free seating with a small selection of reserved premium tickets). The newest confirmed booking is Toby Keith on June 14, on the Corona Grandstand Stage. It’s only his second time at the Fair (he usually plays Chula Vista), and last year’s appearance was cited by many as the highlight of the annual event. From “Should’ve Been a Cowboy” to “Red Solo Cup,” few country acts know how to build, grow, and maintain a faithful audience for as long and successfully as Keith has. If you think going from huge outdoor arenas to a county fair is some kind of career digression, you obviously haven’t been to a fairground concert lately. There are legacy acts putting their grandkids and great-grandkids through college with the cash earned between booths hawking fried Oreos and funnel cakes. To “end up” on a Del Mar grandstand stage is no more of a failure than taking a break between full-lengths to release a greatest hits album. When that many people are offering you money to hear the same hits over and over, giving the people what they want is more sell-through than sellout.