Ask HN: Need advice for consulting (market research)

Branching out to offer freelance market research - in addition to 9-5 day job of similar nature. Consists of a mix of conducting competitor analysis, user research, and quantitative reporting - surveys, prototype testing, etc...

Specifically, I'm focusing on new products and companies (startups included, of course). Does anyone have any suggestions for best practices, helpful resources, examples of things not to do? I have one client I'm speaking with (via UpWork), and they just notified me that they don't actually have the "funding" to pay me until the end of this month. So here's 10% in the mean time.

Worst case worse, it's one more project for the portfolio, but it would still hurt to not get paid.

Failing that, what's been your current experience as a freelancer/consultant?