As I understand it, historically a key function of guilds was to provide a barrier to entry. A guild structure could dramatically cut down on the number of people "accredited" to provide RPG content, increasing the salaries of guild members by preventing everybody else from working in the industry (including those providing content for nothing).Yes, a guild-like structure or accreditation program for creative talent that had actual, meaningful standards as a condition of membership would be helpful, if only as a guideline for the potential employers. It might cut into some executive compensation an/or add a few pennies to the market price of the product, but I’m willing to pay a little extra for quality. Quality matters.
Also, I'm not sure how you determine "quality" in a role-playing product. Pretty much every time I have have panned something on the internet there have been people willing to defend it. I had an incredibly bad (over) reaction to the 4th edition Dark Sun adventure "Marauders on the Dune Sea" - by casually including a running stream in a Dark Sun adventure it felt like WotC had somehow personally insulted me, yet it is averaging 4 stars on Amazon UK and most people seem perfectly fine with it.
Conversely, a great adventure (in my opinion, obviously) like "Mines, Claws and Princesses" gets rated by some people as "impossible to run unless you put in a great deal of work yourself" since the room descriptions don't have any boxed text to read out to the players. (I never read out boxed text anyway.) The adventure itself was written because the author thought the 3rd edition adventure Forge of Fury didn't live up to its potential so wanted to do "Forge of Fury done right" - yet lots of people think Forge of Fury is one of the best D&D adventures ever written.