In 1990 I was asked to guide by a friend who owned a tour company and since have guided a few times a year, mostly single days for individuals, but also for brand name tour companies.
I have no scientific qualifications or background but I had learned my birds and I could speak Chinese so I was able to guide in China as well as HK. Language skills plus the ability to think on your feet to solve problems of varying degrees of seriousness is essential.
I totally agree that the people skills are as important for birding and that showing consideration for , and an interest in your clients as people, and communicating your passion is what people respond to. Many of my clients have been retired and consideration for their fitness levels is important - its all too easy to spoil a great day by pushing just that bit too far at the end - walking an extra 2km in the heat when knackered can whip the gloss off a good day - no-one likes to feel old!
I do it because I enjoy sharing HK, China and the birds with my clients and because birding is my basic state of wakefulness - I love it! Even when I'm not adding new species myself, showing others new birds for the first time allows me to rekindle the excitement and enjoyment of common and familiar species. However I have never pushed that extra step to start a tour company because you answer 50-100 emails per person you take out and there can be a mountain of other admin to running any small business. I have no interest in this so I don't advertise, but let business come by word of mouth.
Expectation management is also essential - he that over-promiseth goeth first and fastest to the wall. If a client sends me a hit list, I will offer my assessment of the likelihood of seeing the birds within the timeframe and budget. I've learned to my cost never to guarantee seeing a bird.
I also set the expectation of my own ability - I'm not the best with calls - especially in parts of China I've visited rarely (sometimes never before), and I'm prepared to say this at the utset and to admit immediately to a cock-up in ID or logistical arrangements. So far none of my clients has expected perfection and because I don't promise it, they don't hold it against me. Most good birders are all too aware of their own falliability!
Other helpful things are learning when your client wants you to find every bird for them, and when to let people find and identify birds for themselves, with a minimum of guidance. Some even enjoy learning how the guide finds and identifies the birds and how to put this into practice.
I think the suggestion to get in some practice by guiding people round your patch or on outings for your local group is a great one - you'll soon find out if you have the combination of patience, confidence, humility and competence to do it and enjoy it.
A bit off the topic of how to start, but reading some of this may help to set your own expectations and build up the skillsets necessary to be a guide.