I understand why you would think something should be done to prevent issues and to make GBs safer to join(in terms of a guarantee you will get the product), but you run into issues with gatekeeping people who have great ideas, and the ability to run them because of a questionnaire or the like, not being "up to snuff" for those who see it. Also the issue of forcing lesser known people to run through the more known runners doesn't guarantee any higher chance of success(look at the alps switch GB ran by novelkeys that failed because the guy never even bought the boards to get the switches). Then you run into the issue that not everyone who is well known can be trusted 100%(Ivan anyone?), and that can destroy a buy that would have been successful had the new runner not been forced to work through a previously considered trustworthy person.
Only thing that will come from limiting is a downturn in the market for customs and keyboard products made by forum members, it will only shift to established, well known stores and that isn't how a niche, hobbyist community should be. Maybe having a set of known GB runners be interviewed by the mods/admins and being put into a group that can support and help newer runners to mitigate the risks? They would have some type on badge on the site and have to do the work either for free or a very, very small fee to prevent greed or a pay-to-play atmosphere to selling a product you came up with. But even then it may still fail, but that is the risk of selling/buying via a forum and there is no such thing as a guarantee when joining a GB, as **** can happen that was out of the control of the GB runner or even the "team" of "pros".