Hi Sz!
Thank you for your suggestion, I recommend next time attaching a pole so you can see how the community feels about it.
As for the suggestion, I don’t think this is needed, if one refuses to request a mediator, they might have Ill intentions and you should back out of the trade. If they do not know about the mediation process, simply advise them of it, provide them the links and proceed with asking the OP to requesting a mediator.
Allowing everyone who posts on a topic the ability to request a mediator will cause extreme amounts of confusion especially for users who bin an item, expect the trade to go through, only for the OP to back out the trade. This will cause unnecessary overhead.
The current system works.
-Krawk