When being asked to serve in an advisory role where you are not being compensated and will not have authority (I.e. Like a board member) you still should ask some fundamental questions. You are in effect exposing your credibility to how this business operates in the market and how market sentiment will impact you.
You want to identify some sense of financial health (you would be getting this by default if you were being compensated as an advisor)
I would suggest speaking to a board member will be beneficial
I would also do some homework to establish your own sentiment on this company if they have any public visibility (including searching for their team members on social networks)
- who are competitors
- how do you differentiate and head off roadblocks set by more established competitors
- what is your position in funding and when do you need additional rounds (impacts how your recommendations can be put to use in realistic fashion)
- who are you trying to reach, both influencers and prospective customers
This should give you a beginning picture of the company and help you decide if you can really help.
I've both recruited advisory boards and served on those boards as well as serving as a board member.
I'd be glad to dive into specific due diligence or other factors if you have more specifics about your possible participation. Glad to hold a brief call to discuss.