Yes, I've had hobbyists / rich kids / astute business-men under-bid me, and if you lose the job, then it's just tough.
However, if the client goes on about how they love the care you put in, and your sound-quality, and then drop you, it can grate. But then they may have overwhelming financial reasons.
However, if the client goes on about how they love the care you put in, and the sound-quality, and then drop you, it can grate. AND ... if you are doing it cheap as a bit of a favour (as it's interesting work, not usually on a Friday or Saturday) — and they STILL drop you ... then you're into the realm of personality, politics or the client just fancies a change, which is fair enough.
So keep soldiering on, keep up the good work, price not-too-cheap, and take on any other work there may be, from wiring to mowing grass to bar-work. Actually, bar-work or waiting (on table!) is essential training for an engineer: Being polite, doing a good job under stress, and dealing with loads of different people.