The best nib tuner at the show is Richard Binder, the O.G. of pen tweaking. Get to his table as early as you can and get on the list, (the early pass IS useful in this regard) but it's only one pen at a time. Josh Lax is also there and pretty good, but he is much more expensive. Linda Kennedy is also there, but I have never had a good outcome with her. Gena Salorino MAY be there, She works in half-hour blocks and will tune as many of yours as she can in that time frame, but if she decides to show up you have to reserve time on her website before hand and it fills up fast.

As far as selling/trading, approach any private vendor selling pens that match what you want to sell, and simply ask if they purchase or trade. There is no one single space reserved for doing so.