Okay so obviously, you can only be one or the other. However once you've been both, even if you can't access the shop of one, both do still remain open and you can still make sales from the class that you do not have access too.
I personally am currently a merchant and considering changing back to rancher but trying to figure out when the prime time for myself to do that would be. It would help if I could see what sales I have made in my rancher shop while being 'away'. I have been keeping tabs of how many creatu I have in my shop and how many slowly disappear but I never know which ones.
On that note - I also find it a pain in the butt that I have to go through my profile to my rancher to be able to view it and i can't just click on rancher shop from the drop down shop menu (Lazy I know).
So... I propose the idea of ghost viewing. You may look at the shop of the class you currently don't have access to, to see how it's going.
Nothing else. Just simple viewing.
Still can't change prices, pick up the money from the till, add or take away stock. Just view. I think this would be a nice little perk that could possibly even make more people think about changing classes more often which would be good for the res economy.
Could potentially even make it an item?