Ding Dong Plumbing Company

This really only matters if you have a preference, but it is good to ask. If you have a strong ideological belief about unions or nonunions, it's perfectly acceptable to make a decision based on the preference.

You'll always want to ask how long the company has been in business in Los Angeles. While this isn't a guarantee that the company will do good work, companies with longevity on their side must be doing something right. That being said, there are newer companies that do great work. If the company is under three years old, ask where the owner was employed before and for how long. If he/she has a long history of employment, it's reasonable to infer that he or she decided to go into business for themselves after so many years of experience.

This will be answered when you ask if all employees are licensed. The only way to obtain a legitimate tradesman's license is to be a legal or naturalized citizen of the US. The company may employ people in positions that don't require a license, however, so it's wise to inquire.

Always ask for references, and always check them. Keep in mind though that the only references you'll get are people who the contractor is certain will give him a good review. You'd also be well advised to check online review sources in Los Angeles as well, which will give you a broader view of customer satisfaction for a given company.

You'll certainly want to ask them this. Steer clear of any company that is not insured in California, because that means that any incidental damage they may do on your property will be a real hassle to recover compensation for. It is never wise to work with uninsured tradesmen of any kind. Most states also require that someone have insurance in order to be issued a trade license. If they say they're licensed but not insured, they're being less than truthful.