Is this a problem? This sounds like ordinary business development / product management. Let's say I started a cloud provider. A customer comes to me and says "we need something like BigQuery". The first thing I'd do is sign up for BigQuery and try it out, right?
If you're making an online marketplace, you probably want to try using other peoples' online marketplaces. Make sure you're not missing something obvious. Implement their good ideas, rework their bad ideas. That's competition.
As far as competitive intelligence goes, this is pretty small stakes. In the industrial space it's pretty standard for major companies to create shell companies that buy up competitors' equipment and do full clean-room teardowns that result in engineering reports handed off to the designers back in the parent company. One can certainly argue as to whether this is dirty pool or not, but it's standard practice and everyone's factored it in as part of competition.
Right, exactly. This is like those companies that buy new cars, tear them down, and sell anyone who wants a 1200 page report about all the new technology in the car. Frankly, I think you'd be crazy to not understand your competitors technology in depth. They might be onto something. If they don't want you to steal it, that's what patents are for.
This process seems a lot more ethical than, say, hiring an employee and "hoping" that they'll have the same thought process at your company that led them to an innovative trade secret at their former job.
Even that second thing is fair game in my opinion. You got some people with valuable thoughts in their brains, maybe you go to great lengths to keep them happy.
It's not quite an employer/employee relationship, just a partnership. So this is kind of like starting your own video streaming website while being a Twitch Partner. I don't know if the T&C prohibit that, but they would probably be difficult to enforce.
I feel like the courts would take a dim view of "if you ever sell a trinket on our platform, you are banned for life from ever working on e-commerce", but I guess you don't know until you try.
If you're making an online marketplace, you probably want to try using other peoples' online marketplaces. Make sure you're not missing something obvious. Implement their good ideas, rework their bad ideas. That's competition.