If you’re not a software developer, to create a marketplace you’d have to hire or partner with one.
Even if you had a great idea, without the tools and expertise to create the platform, you’d be stuck on day one.
Even if you managed to assemble a team of developers, designers and software specialists, there are still months and months of ideation, wireframe creation, producing a Minimum Viable Product (MVP), beta testing, bug finding and revision ahead of you.
All in, it could take anything from a year to two years to go from your big idea to a product that was ready to publish and launch.
This means there are probably a lot of great marketplace ideas lying in a drawer somewhere!