Dukman
I was wondering that as well.
Personally I think that would get annoying really quick. And I have yet to spend any caps on anything. I have enough crap stored that I can straight up trade enough of it for what I need. Usually what I get from merchants is ammo that I have a hard time finding. (.308 and shotgun shells) and rarer crafting materials. But the merchants so far haven't had anything that I just have to have. I can almost always build what I need or want from stuff I looted.
"Personally I think that would get annoying really quick."
I agree with you on this, especially if you have to look through tall grass to find the coin(s).
For me, I have plenty of 308. My shortage happens to be in 5.56 and even more so shotgun shells. When I come in with a load of loot to sell I look for those 2 item first. If they have it, I sell and buy the ammo.
Just out of curiosity, have you noticed that you can not get any items that are copper, steel or any of the many other bulk items that are listed under "shipping" from merchants that you establish?