Your hiring a contractor.
Your looking into a dog walking service.
Your putting a loved one in a "retirement community"
Your partnering with another business.
Your looking to purchase something on the Internet.
Your investigating a person or company.
Your considering using a company your unfamiliar with.
The reasons are ENDLESS. The fact is, any company with a little cash can put out a commercial, a pay per click ad or other means of getting your attention. That doesn't mean they're trustworthy. Companies pop up every day and companies shut down every day. Check them out with a few simple steps.
If they don't have a physical address listed online, that's a red flag right off the bat. If they do, search corporate records in that state. See how long they've actually been around. See if they are doing business as a different name than their legal name.
Then search "DBA" (doing business as) names, "Fictitious" business names and their legal name through Google. Look for comments made by people online via blogs, newsgroups, and sites such as the the Better Business Bureau , Ripoffreports.com, Yelp, and other consumer review sites.
If the corporate records list the principals of the companies, search them through the same means but go a step further. Run their names through any criminal record and civil litigation searches available in the states they do business in.
Be proactive not reactive, it will save you a lot of misery!