Have been playing for a very long time now and yes sometimes people craft at a marketboard but no the vast majority dont do it on purpose. Why move when after buying the last piece you need for a recipy to craft it?
Also it happens hardly at every marketboard, to be honest its more of an exception that happens then a rule.
Personally i find another player crafting sounds irritating when i try to craft myself but thats where i just move so i dont hear it.

As to a toggle for crafting sounds, that's only possible if they are handled as a category by itself. Also now its crafting sounds next time its lalafel's emote spam, one specific skill sound and you could go on. What i want to say here is where do we stop putting in toggles for this or that? When does it become too much work to put in all the options?
If its very easy to do sure do it but we've learned that when it comes to coding its never that easy to do.