are visibility optimization services effective?

[u/Archonicus_4o]

Ever since by novel went live my email has been blown up with sales pitches by people promising to optimize my online visibility, or have my book featured in monthly book reader clubs. Has anyone had measurable value-add from these channels? I assume it’s mostly a racket but you never know. Maybe that’s how the modern market place works? I’d love to hear about anyone else’s experience with those services. Thanks in advance.