Even if you are working alone, there is no excuse for not being agile.
I'm a freelance, working alone from home, and I use a combination of agile methods with great success. Scrum in itself is good for a single person, but need to be adapted. For example, a standup meeting or a planning poker alone is not funny.
The most useful practice, in my opinion, is splitting project into fixed time iterations. Work two weeks. Deliver partial product. Get paid. Start again. You don't need to have a big team to work with iterations, right?
Always getting feedback is also very important: make sure that your client is always as happy as possible.
Use stories to feed your backlog, and have your client sort it out by priority: priceless.
Other methods can be added for more efficiency: TDD, pomodoro, etc.
Sometimes, I happen to work with a friend when I get too much work. If you already use a Scrum canvas, adding another person in a team is quite easy.