When it comes to market selection, I often think back to how Ryan Petersen came up with the idea of Flexport. He put up landing pages and some ads, and only when he saw interest from the biggest players did he go all in. It's a pretty darn good way to find out, even if it sounds too simple, or cheap, but if you listen to the rest of the interview, Ryan had semi-failed enough times beforehand to realize that simplicity was key. Maybe throw a bunch of landing pages up and see what works?

(original audio segment: https://smashnotes.com/p/y-combinator/e/92-ryan-petersen/s/h...)