You get to set the requirements for the people you employ or hire to do work for you. You can require background checks.
Yes you should whether it is required or not. One of the contractors may get injured on the job and decides to sue you for damages whether you are responsible or not. So make sure you have all licenses and insurance.
contractors
By using the term withhold, I suspect your intending to ask what Cos withhold employees income tax from pay. It doesn't have to be a company, officially, in any way. Any pay to an employee (rather than to someone who works as an independent contractor - which in itself requires certain things be maintained - MUST have withholding (and the matching FICA contrbutions, etc) by the employer. So, for example, if you employ a nanny, or an elderly person a caretaker on your own, as many do, you must provide payroll withholding and reporting.
safety and health
Yes, There are some insurance companies and some individuals that utilize the services of independent appraisers.
The Americans with Disabilities Act.
Yes Lens Crafter's does employ certified optometrists. Lens Crafters is one of the best nationwide optometry chains. Most LensCrafters locations do not directly employ certified optometrists. They will usually have an independent optometrist office located within their facility. They are associated, but still independent from each other.
In 2011, Boral employs 15227 people on site, 5,600 people which are full-time contractors working across global operations.
Usually stores such as Sears have contractors that they employ to provide services such as this. I am not sure about vinyl siding on windows, but they do have contractors that install vinyl siding as well as windows. You can inquire at your local Sears store as to the cost of installation.
Yes, only the employers and not the employees. However, there are classes of employers not subject to payroll taxes if they employ independent contractors, or some seasonal work, etc. Each state decides its own classification.
Each Erickson community has their own Independent Board of Directors and Executive Director.