How Can I Ensure My Book Is Free of Errors and Ready for Publishing?

I’m almost done writing my book, but before I move forward with publishing, I want to make sure it’s completely error-free and polished. I know proofreading and editing are essential, but I’m wondering—what’s the best approach?

I’ve seen some book writing services in USA that offer editing and proofreading, but I’m curious if anyone here has used them. Do they really catch everything, or should I also hire a separate editor? Also, what’s the difference between copy editing, line editing, and developmental editing, and which one is necessary before publishing?

For those who have already published a book, what worked best for you? Did you use professional services, beta readers, or software like Grammarly? I’d love to hear your tips on ensuring a book is 100% polished before it goes out into the world.