1. See the company
If possible, visit the Headquarters, talk to anyone you can get hold of.
2. Check license
Verify the business has business license from the city, county and state agencies.
3. Find out any litigation
Search the company's current and past names and see if there is any lawsuits and bankruptcy filings. Court filings can be found at www.pacer.gov.
4. Read financial statements
You should ask for corporate tax returns.
5. Evaluate investment
Make sure you are aligned with the business' short term and long term plans.
6. Understand the future
Check how much the company needs, not just this round, but also in the future.