Before you think that finding the right coach automatically means the best results possible, you have to keep something in mind. The coach is not forcing your to follow your diet or train as optimally as possible. They will give you the professional advice and guidance needing to get you where you want to be. However, it will still come down to your effort and how bad you want it! A coach is not your chef and is not your drill sergeant 24/7. You'll have to stay motivated when you aren't talking to your coach!
So, what makes the perfect coach? There isn't a one size fits all coach that is perfect for everybody. There will be some that have great experience and get their clients great results, but they don't cater to your specific goals! You have to keep this in mind when looking for a coach. Find someone who is experienced with coaching those who have very similar goals to yourself. An example of a high quality coaching program is here: http://mmfitstrong.com/online-fitness-coaching
Here are a few things to look for:
Qualifications - I touched on this already. Having a certification or a degree does not automatically make someone a great coach. However, it does take the overnight gurus out of the picture a bit. I don't care how in shape someone is: if they are not willing to get certified, or a degree, then they are not committed to their profession and you can do much better!
Experience - Great coaches typically aren't great with their first few clients. It takes time and experience to build a solid coaching foundation and making sure their programs and plans are fit for their clients. A lot of online fitness coaches are local personal trainers too. The best of them have trained hundreds of people in their careers. This experience lends itself to a better experience for future clients. Simply put: get a coach who has plenty of experience and testimonials/case studies from their clients to back up their experience.
Walk The Walk - I'm sorry, you can't be taken seriously unless you look the part. I know, having a little extra body fat doesn't mean that person doesn't have the knowledge to get super ripped. However, if that person has never put their own advice to use, that is a good sign of a bad coach. I don't think you should take advice on getting to single digit body fat percentage if that person giving the advice has never gotten there themselves. They don't have to be the strongest, biggest, most ripped person in the gym, but they should actually look like they know what they are talking about!
Personal Connection - You need to build a solid relationship with your coach if you want to succeed. It's more than just giving you a training plan and diet to follow. A great coach connects with each of their clients to build a great foundation to lead to better results. A coach who really gets to know you and understands your lifestyle and beliefs will get you better results. Don't settle for a coach that sends you programs and never talks to you again until it's time to renew your contract!
Don't settle for the popular coach, either. They might be great marketers, but terrible coaches. Get to know your coach, read their publications, and make sure you agree with their philosophy. Butting heads over training and nutritional protocols should never happen with your coach. You have to trust your coach and trust their process. If you don't respect the coach enough to trust that, they aren't the right coach for you! If you are willing to spend the money to hire a coach, make sure you aren't wasting it on a coach you aren't compatible with!