I understand Google and Facebook are aggressively doubling-down on the advert spend coming from bricks and mortar retailers, to try and show the '$' contribution to in-store sales. If I wanted to beat them at their game with a in-store analytics app, which tied retailers' online ad spend with in-store sales, how would I best validate customer demand without it costing a small fortune in market research?
If you already have something developed that does what you say, then you could walk door to door at retailers around you and introduce yourself to the manager and give them a trial version and show them how to use it. Then go back to visit a couple weeks later to ask how they like it.
While you're there ask them what websites they read to keep up to speed on marketing stuff, analytics stuff, etc. Then go to those websites and post things there, or see if you can advertise cheaply there to reach others within that audience.
In the process of this you should be getting a feel of the persona of the person that you're selling to (the person that would actually do the buying of your product, not necessarily the end user, although that's useful to know too). Use that info to make tailored ads on Facebook, etc.
The feedback you get from all of this is your market research.
Hmm...this is a loaded question. First, by customer, I am assuming you mean B&M(Brick and Mortar) shop owners. Well I hope you did, because my answer will be geared towards this "customer". Ok- Facebook aside, if I were tackling this question I would ask, "How is the B&M currently attributing in-store sales?" If they are not even tracking it, then why would they be interested in your service? If they are tracking it, but it is independent of the FB ad spend, then a.)what factors do they believe should be attributed to in-store sales, and b.)what was their original goal and purpose for the FB campaign and are they actively evaluating their ad $$? I believe first figuring out what/how each customer is currently tracking it's data, will give you insight on whether or not they have a "demand" to know the FB ad vs. in-store sales correlation. But I will throw a wrench at you, there are numerous articles and research stats/papers out there which speak to the fact that online sale and B&M sales are almost always independent of each other. When tied into an omni-channel approach, this is when you can begin to correlate such independent data sets. However, if the B&Ms are not using omni-channel strategies- then the concept of your application is kinda moot. I believe showing the contribution of FB ad spend versus online sales, would be a more direct approach to your analytics application.