Just chiming in real quick as an old timer and veteran of Trade Corner...
Honestly, I don't see what the big issue is in not allowing this to happen. Not trying to step on anyone's shoes here, but I mean all she's asking for is a direct way in which she can respond to people's trade reviews, which personally I applaud her because back in my day I don't remember anyone who did that. Yes, there's a like system that can be implemented and yes, you can VM/PM the person, but is it really that big of a deal in not allowing this? It's not like it's overthrowing the system or anything; it just allows a new outlet in which the owner can communicate better with their customers.
Allowing this sort of thing is not going to turn Trade Corner into a spam pit. Instead, it's going to allow relationships between users flourish and grow and create a better sense of a community within a community. If there really was an issue, that's what the report system is for. Simple as that. She's even willing to meet y'all in the middle in regards with that - i.e after every 10 replies - which I personally don't think a handicap even needs to be placed, but that would ultimately solve your worries of a spam pit forming.
In the end it's ultimately up to the moderators of the section to make a decision. But considering the amount of suggestions that I've seen flow by this section, this is one that I personally see as pretty harmless.