Hiring care workers is an unavoidable part of living with ALS. It's one part of the disease no one tells you about--that you must become an employer. If workers are paid, remember that they are care workers, not care "givers." No matter how close they become, they are in it for the money and will not be as loyal as family caregivers. Many of the people in this labor pool who call themselves "professional caregivers" are looking for easy jobs babysitting the elderly, and it is not uncommon for them to jump ship without notice when they learn about an easier job, or when caring for your PALS starts getting too hard. So it's good to have more than one worker, so you do not suffer a total loss when one of them quits without notice.
We tried several agencies, and I will never use another agency again. Agencies all recruit from the same labor pool. You can get access to the exact same workers by posting a want ad on indeed.com, and it will cost a fraction of what the agency charges. Also, you can pay them more than they will get from an agency, which can reduce turnover. Many workers like to be paid under the table, but it's best for you and them if you pay them on the books. If you don't know how to do payroll, try to find a friend or family member who does, and ask them to help you.
If you don't have trained backups, you need to be ready at all times to step in when they call in sick or quit. This is true even if you hire an agency--they will promise backups, but the reality is they do not have backup people trained to deal with ALS patients. Again, if you have more than one trained worker working regular hours, it will help a lot.
At first, the job is probably totally unskilled. As the disease progresses, more nurse-like functions are added, first as an incidental, then later, more substantial part of the job. Administering medicine, tube feedings, operating a BIPAP and cough assist machine, require increasing skill and focus. If you hire a CNA, they may get freaked out and quit when these duties start to increase. In our experience, the perfect care worker for the job is a "practical nurse," which is sort of a cross between a CNA and a registered nurse. These are people with a community college education who are interested in a career in health care and will welcome the medical parts of the job, rather than being daunted by them. You don't need to pay them much more than a CNA, and it is well worth it. Also, as nurses, they cannot ethically abandon their patient, and so they give plenty of notice and train their replacement before they leave to pursue their RN degree.
So bottom line: Our situation has been reasonably happy and stable since we have hired practical nurses through the posting of want-ads on indeed.com, and having an out of town family member doing the payroll.