Technically, there IS a GUI.
It's the console's command line. Just open the console and type the line of code that commands the Game.market API to do what you want. Things like create an order, or buy an order through a deal are simple one liners.
Sure, the big hassle is that you can't be ON the market page and have the console open at the same time, but the clipboard works for capturing the id of the order you want to interact with. Anything else you can scribble on paper.
I mention this because it's not always obvious that you can just enter API code directly into the console. If you're like me, and had NO JS experience when starting, I didn't know you could do that... instead I wrote some stupidly complicated function to "single shot" a line of code into the market.