Never let your players manoeuvre you into a situation where your players know the rules better than you (as DM).
It can be pretty had to tell if something is unbalanced until you actually see what your player does with it.
Then I would never DM with my current group. Which would be sad, because I quite like them.
I started DMing at the end of 2014 after not having played TTRPGs since the early 90s (and not D&D since the late 80s). All of my players, however, have been playing continuously since the 80s. Most also play D&D and other games several times a week. A couple DM regularly for other campaigns. Currently my schedule allows me to prep for and run my once-per-month 8-hour session.
There is no way that I can avoid a situation where the players know the rules better than I do, unless I run a different system.
In terms of *rules* I take a "judge" approach to my role as DM. I expect that that players will know many rules better than I do--especially those pertaining to their characters. I expect that I can call on them to help with determining the rules for less common situations. Where things are unclear or don't fit the current situation, I, as DM, make a judgement.
Where I have the luxury of time, however, I do like to read discussions on various scenarios and put out questions to the ENWorld community. It helps me discuss options with my players and, most importantly, I enjoy discussing these things.
But I don't kid myself. My one mediocre brain isn't going to out-think the combined powers of 4-6 much more experienced players.