I am a voiceover artist full time and have been for 10 years, with a professional home studio for that duration.
Without sounding condescending, an afternoon course is never going to teach you everything you need to know about becoming a successful voiceover artist. You may book a few gigs, but to be good enough to sustain an entire career... there is no way.
There seems to be an upsurge in people flogging VO work as a way to make a quick buck and of course anyone can buy a cheap microphone, record themselves speaking the lines and send it over, in essence this is what a voiceover is. But to sustain a whole career you also need to be good at it. You need to be able to take direction for a producer/director/creative, you also need to k ow how how self direct, learn how to control and manipulate your voice, learn how to perform different styles of VO (narration, video games, elearning, explainers, animation etc all have different styles and expectations of your voice), you need to know how to find good work that isn't undercutting the rest of the industry (and no, the no-vetting pay-to-join sites are NOT the way in), you need to understand your equipment and be able to provide specific audio and mastering to your clients, you need to invest in high quality audio equipment (NOT a USB microphone with a duvet over your head), you need to create a professional Web presence and scout for good clients, you need to be your own accountant and cheerleader cos you're in this alone, you need to spend time practicing accents, styles and Copy, recording 100s of auditions that you'll never get, and staying up to date with what is current in the industry.
I have received so many 'people tell me I have a nice voice' emails over the years, but a nice voice isn't enough. You have to want to do this, commit to it and tbh you need to have a talent for it. I also went to drama school for 3 years and have an acting degree, so my training (especially vocal training) from that is invaluable to me. Living in London is also massively useful to me as most of the jobs through my agent are in town.
Sorry to be such a Debbie downer, but all these 'pay me £150 and I'll teach you to be a VO' courses are very fustrating and unrealistic!! What were you taught in the course? Was it online?