This topic brings to mind another red flag - GMs who make something difficult through IC means, and then get upset when the players try to defeat that difficulty, because what they really wanted was to ban it on an OOC level and/or have it require a plot-based solution. Look, most of D&D gameplay is overcoming challenges. If I were playing a character who gave up when something wasn’t immediately easy, I wouldn’t be adventuring in the first place!

So when I see a magically locked door, I’m going to see if we can take it off the hinges, or enter from another spot, or one of the many other ways to deal with such an obstacle. I’m not going to immediately give up and go look for a sage to send us on a quest for the magic key - why would I even assume that’s possible? If you want that to happen, create a situation where it makes sense IC or just say so OOC (I’m not a fan of skipping an obvious solution for plot reasons, but I’ll do it once or twice, especially if the GM is new).

Likewise, if you say there are no magic item shops, that doesn’t say to me “So don’t bother ever trying to acquire magic items”, that says “So you have to go do the legwork yourself”. If what you really wanted was low-magic or GM-controlled access, then say so OOC. I may or may not want to play that way, but at least I won’t be wasting everyone’s time on something that’s secretly pointless.