What is the best way to validate a B2B2C idea?

If you are really thinking about building your product you should first do the alpha and beta. There is a strong community of tech people on Hacker News, ProductHunt and Reddit that will support your idea and even pay in advance if you can show a demo first.

Give you an example: Dropbox. Drew (CEO) made this short video https://www.youtube.com/watch?v=7QmCUDHpNzE about how Dropbox was supposed to work. He send it to all the community and it becomes viral. Everyone started to sign up. He had a fremium model at start, but look at it now.

So I will encourage you to do two things:
Follow this order
1-Go and build your alpha/beta and create a demo that everyone can see and feel excited about
2-Share it with the community
3-If you want to "sell it" in advance you can use selz.com or payloadz.com

And rethink you business model and moentization strategy so it adapts to your product and not the other way.

:) If this helped let me know!

Looks like an interesting service for sure in the form of a browser extension. I guess my first question would be, are you validating it to raise capital eventually? Do you need capital now to ultimately create it? From the sounds of it the best way to validate it if you have the option is to create it and have people use it.

If you don't have that luxury, is there a way you can validate it manually? Sounds like a stupid question but sometimes you might be able to validate an idea through manual means first then develop the technology around the process to replicate the result automatically. Hope that helps!