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.